Non-steam-curing UHPC (Ultra High Performance Concrete) based on P.O42.5 and with low cement consumption and preparation method of non-steam-curing UHPC

Abstract

The invention discloses a P.O42.5-based steam-curing-free UHPC (Ultra High Performance Concrete) with low cement consumption and a preparation method thereof. The UHPC is prepared from the following components in parts by weight: 100 parts of cement, 13 to 30 parts of silica fume, 5 to 13 parts of fly ash, 149 to 181 parts of quartz sand and coarse aggregate, 18 to 23 parts of steel fiber, 2 parts of a water reducing agent and 22 to 26 parts of water. The preparation method comprises the following steps: carrying out dry mixing on the fine aggregate and the cementing material in a mortar mixing pot; uniformly mixing and stirring water and a water reducing agent, pouring the mixture into a stirring container, and starting wet stirring; after the mortar is in a flow state, continuously stirring; and adding the steel fiber and the coarse aggregate, and stirring to obtain the ultra-high performance concrete mixture. According to the invention, P.O42.5 cement commonly used in a construction site is adopted, basalt macadam and large-particle-size quartz sand are introduced, and coarse aggregate and different-particle-size quartz sand grading are adjusted, such that closest packing is realized, high strength performance is realized by giving full play to its skeleton effect, cement consumption is reduced, and construction cost is reduced. And the method can be applied to severe environment service or lightweight structure design.

Description

Technical Field

[0001] The present invention belongs to the field of high-performance concrete, and in particular relates to a low-cement-dosage, autoclaved UHPC based on P.O.42.5 and a preparation method thereof. Background Art

[0002] Ultra-high performance concrete utilizes the tightest packing principle for mix design. By optimizing the compatibility of the water reducer with the cementitious components to enhance the matrix's density and fluidity, and incorporating 1% to 3% by volume of chopped steel fibers to increase its toughness, ultra-high performance concrete can be cured using conventional, steam, and even pressurized steam curing systems. It exhibits excellent workability, exceptional durability, toughness, and long service life. Compared to conventional concrete, its ultra-high performance is reflected in two key aspects: superior mechanical properties and exceptional durability.

[0003] Compared to high-performance concrete (HPC), ultra-high performance concrete (UHPC) not only achieves further high reinforcement, but also creates a new collaborative working mode due to the introduction of steel fibers. Under load, especially under tension, the components can exhibit significant strain hardening characteristics. From the perspective of stress-strain constitutive analysis, after the component cracks under tension, the curve enters a plateau section, showing a behavior similar to the yielding of steel, rather than the brittle fracture characteristics exhibited by high-grade concrete. In addition, UHPC configured with a 2% volume content of steel fibers has high shear, flexural, and tensile strength. When designing structural components, the amount of ordinary steel bars can be appropriately reduced, forming UHPC beams with few or even no web reinforcements. The shear resistance of the UHPC matrix and fibers alone can meet engineering requirements. At the same time, the structure with less steel bars allows for a uniform distribution of the UHPC steel fibers, preventing dense ordinary steel bars from affecting fiber orientation or even agglomeration, which is beneficial to the performance of UHPC.

[0004] Ordinary concrete materials are inexpensive to produce and have mature construction technology. Although they can meet the needs of various construction projects, they are heavy, have low tensile strength and poor toughness and cannot meet the needs of lightweight, assembled bridge structures and the development of larger spans. Steel structures are also expensive and require a lot of painting, maintenance and repair work. Using ultra-high performance concrete materials UHPC to replace ordinary concrete materials for structural innovation can further reduce the weight of the beam structure and meet the needs of lightweight and assembled engineering structures. At the same time, it has ultra-high durability and can be maintenance-free throughout its life cycle, reducing subsequent maintenance costs.

[0005] To improve the strength of ultra-high performance concrete (UHPC), existing technologies often use high steel fiber dosages, steam curing, and even the addition of nanocrystal seeds to achieve high strength. This increases project costs and is not conducive to its widespread application. In addition, existing UHPC configuration technologies generally use high-grade cements such as PO.52.5 or P.II 52.5 to ensure the 28-day strength of UHPC. This requires the separate purchase of high-grade cement at the construction site, increasing procurement and storage costs and hindering the application of smaller volumes of UHPC on-site. Therefore, it is urgent to research low-cost, steam-curing-free UHPC material configuration technology based on the commonly used cement grade, namely PO 42.5 cement, and to minimize cement usage to improve crack resistance. Summary of the Invention

[0006] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a steam-cured UHPC based on P.O42.5 and low cement dosage and a preparation method.

[0007] The technical solution of the present invention is: a non-steamed UHPC based on P.O42.5 low-cement dosage, ultra-high performance concrete, comprising the following components in parts by weight:

[0008] 100 parts of cement,

[0009] 13-30 parts of silica fume,

[0010] 5-13 parts fly ash,

[0011] 149-181 parts of quartz sand and coarse aggregate,

[0012] 18-23 parts of steel fiber,

[0013] 2 parts of water reducing agent,

[0014] 22-26 parts water.

[0015] Furthermore, the cement, silica fume and fly ash constitute a cementitious material.

[0016] Furthermore, the cement in the cementitious material is P.O42.5 Jinyu Jidong ordinary Portland cement, and the storage period does not exceed 3 months.

[0017] Furthermore, the silica fume in the cementitious material is semi-densified silica fume, the mass of which accounts for 15%-30% of the total mass of the cementitious material, and the density is 300kg / m 3 , particle size is 0.1-2μm.

[0018] Furthermore, the fly ash in the cementitious material adopts Class F Grade I fly ash, the mass of the fly ash accounts for 5%-12.5% ​​of the total mass of the cementitious material, and the main particle size is 1-100 μm.

[0019] Furthermore, the quartz sand and the quartz sand in the coarse aggregate are refined quartz sand, and the SiO2 content thereof is above 98%.

[0020] Furthermore, the quartz sand and the coarse aggregate are basalt crushed stone with a particle size of 5-10 mm and a mud content of ≤0.5%;

[0021] The quartz sand is refined quartz sand, which is divided into four mesh sizes:

[0022] 80-120 mesh (particle size 0.125-0.18mm), 40-70 mesh (particle size 0.212-0.425mm), 20-40 mesh (particle size 0.425-0.85mm), 10-20 mesh (particle size 0.85-2.00mm).

[0023] Furthermore, the steel fiber is a straight copper-plated steel fiber with a length of 14 mm and a diameter of 0.2 mm, and its tensile strength is ≥2000 MPa.

[0024] A method for preparing autoclaved UHPC with low cement content based on P.O42.5, comprising the following steps:

[0025] First, fine aggregate and cementitious materials, namely cement, silica fume and fly ash, were dry-mixed in a mortar mixing pot for 1 minute.

[0026] Then, mix the water and water reducer evenly and pour into the mixing container to start wet mixing;

[0027] After that, after 2-3 minutes, when the ultra-high performance concrete mortar becomes fluid, continue stirring for 5-6 minutes;

[0028] Finally, steel fibers and coarse aggregates were added and stirred for 5 minutes to uniformly disperse the steel fibers and coarse aggregates to obtain an ultra-high performance concrete mixture.

[0029] The beneficial effects of the present invention are as follows:

[0030] The present invention adopts P.O42.5 cement commonly used on construction sites. By introducing basalt crushed stone and larger-particle quartz sand, and adjusting the grading of coarse aggregate and quartz sand of different particle sizes, the densest stacking is achieved, and its skeleton function is fully utilized to achieve high-strength performance while reducing cement consumption.

[0031] The ultra-high performance concrete of the present invention can reach a strength of over 180 MPa in 28 days through standard curing methods without the need for steam or water curing. At the same time, its elastic modulus and crack resistance are improved, facilitating on-site preparation and rapid construction, reducing the overall cost of ultra-high performance concrete, and can be applied to harsh environmental service or lightweight structural design. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The particle size distribution of each raw material in the embodiment, the packing curve of Example 1 and the closest packing target curve. DETAILED DESCRIPTION

[0033] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and embodiments:

[0034] like Figure 1 As shown, a low-cement, autoclaved UHPC based on P.O42.5, ultra-high performance concrete, includes the following components in parts by weight:

[0035] 100 parts of cement,

[0036] 13-30 parts of silica fume,

[0037] 5-13 parts fly ash,

[0038] 149-181 parts of quartz sand and coarse aggregate,

[0039] 18-23 parts of steel fiber,

[0040] 2 parts of water reducing agent,

[0041] 22-26 parts water.

[0042] The cement, silica fume and fly ash constitute the cementitious material.

[0043] Specifically, the water-cement ratio of ultra-high performance concrete is 0.18 to 0.19.

[0044] The cement in the cementitious material is P.O42.5 Jinyu Jidong ordinary Portland cement, and the storage period is no more than 3 months.

[0045] Specifically, the cement is P.O42.5 ordinary Portland cement commonly used in ordinary concrete at construction sites, that is, the cement strength is not less than 42.5 MPa.

[0046] The silica fume in the cementitious material is semi-densified silica fume, the mass of which accounts for 15%-30% of the total mass of the cementitious material, and the density is 300kg / m 3 , particle size is 0.1-2μm.

[0047] Specifically, the silica fume has high pozzolanic activity, and its main component SiO2 can react with the hydration product of cement Ca(OH)2 to form a dense and high-strength CSH gel; in addition, silica fume with a smaller particle size has a filling effect, which can fill pores, further reduce porosity and increase strength. Fly ash has weak pozzolanic activity, and its particles are mostly spherical in shape, which can play a lubricating and ball-rolling role. Through experimental research, it was found that with the increase of silica fume content, the expansion degree of UHPC first increases and then decreases. When the silica fume content is small, it can fill the gaps between cement particles, thereby reducing water demand. When the silica fume content is further increased, its larger specific surface area causes an increase in water demand, increasing the viscosity of the slurry. The silica fume content should be between 15% and 30%.

[0048] Specifically, the silica fume should be semi-densified silica fume with a lower density. The particle size of the densified silica fume is large, and it is difficult to effectively disperse it by conventional stirring, thereby making it difficult to fill the gaps between cement particles, and the slurry fluidity is significantly reduced. The silica fume in the embodiment of the present invention is semi-densified silica fume with a density of 300 kg / m 3 , particle size is 0.1-2μm.

[0049] The fly ash in the cementitious material is Class F Grade I fly ash, the mass of the fly ash accounts for 5%-12.5% ​​of the total mass of the cementitious material, and the main particle size is 1-100 μm.

[0050] Specifically, although the addition of fly ash microbeads can slightly improve fluidity, the fly ash microbeads have a hollow spherical structure, which significantly reduces the strength. Therefore, the fly ash described in the embodiment of the present invention is Class F Grade I fly ash.

[0051] The quartz sand and the quartz sand in the coarse aggregate are refined quartz sand, and the SiO2 content thereof is above 98%.

[0052] The quartz sand and the coarse aggregate are basalt crushed stones with a particle size of 5-10 mm, and the mud content is ≤0.5%.

[0053] The steel fiber is a straight copper-plated steel fiber with a length of 14 mm and a diameter of 0.2 mm, and its tensile strength is ≥2000 MPa.

[0054] Specifically, the steel fiber is added at a volume ratio of 2%, that is, 160 kg of steel fiber is added per cubic meter.

[0055] Specifically, the refined quartz sand is divided into four mesh sizes:

[0056] 80-120 mesh (particle size 0.125-0.18mm), 40-70 mesh (particle size 0.212-0.425mm), 20-40 mesh (particle size 0.425-0.85mm), 10-20 mesh (particle size 0.85-2.00mm). With a sand-cement ratio of 1.1, adding large-size quartz sand (10-20 mesh (particle size 0.85-2.00mm)) can effectively improve the strength of ultra-high performance concrete and increase internal restraint, thereby reducing shrinkage.

[0057] Specifically, the water reducer is the 3301 polycarboxylic acid water reducer produced by Sika Company, with a water reduction rate of ≥30% and a solid content of 40%.

[0058] A method for preparing autoclaved UHPC with low cement content based on P.O42.5, comprising the following steps:

[0059] First, fine aggregate and cementitious materials, namely cement, silica fume and fly ash, were dry-mixed in a mortar mixing pot for 1 minute.

[0060] Then, mix the water and water reducer evenly and pour into the mixing container to start wet mixing;

[0061] After that, after 2-3 minutes, when the ultra-high performance concrete mortar becomes fluid, continue stirring for 5-6 minutes;

[0062] Finally, steel fibers and coarse aggregates were added and stirred for 5 minutes to uniformly disperse the steel fibers and coarse aggregates to obtain an ultra-high performance concrete mixture.

[0063] The above curing method of non-autoclaved UHPC based on low cement content of P.O42.5 includes the following steps:

[0064] First, the ultra-high performance concrete is poured and formed, and the vibrating table is vibrated for 5-10 seconds and the surface is covered with a curing film;

[0065] Then, place it in a standard curing room and remove the mould after curing for one day;

[0066] Finally, continue curing until 28 days before conducting strength test. The standard curing temperature is 20±2℃ and the relative humidity is above 95%.

[0067] Specifically, the present invention adopts P.O42.5 cement commonly used on construction sites. By introducing basalt crushed stone and larger-particle quartz sand, and adjusting the grading of crushed stone and quartz sand of different particle sizes to achieve the densest stacking, the high-strength performance is achieved by fully utilizing its skeleton function, while reducing the cement consumption. The ultra-high performance concrete of the present invention uses only 648 kg of cement per cubic meter.

[0068] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples described. Unless otherwise specified, the raw materials used in this application can be obtained commercially.

[0069] Example 1

[0070] This embodiment provides an ultra-high performance concrete configuration scheme, and its raw material formula (weight parts) is shown in Table 1, wherein the cement used is P.O42.5 ordinary Portland cement, and this example uses Jinyu Jidong brand cement.

[0071] The silica fume adopts low-density semi-densified silica fume with a density of 300kg / m 3 , particle size is 0.1-2μm.

[0072] The fly ash used is Class F Grade I fly ash, with a main particle size of 1-100 μm.

[0073] The quartz sand is refined quartz sand with a SiO2 content of more than 98%. It contains four mesh sizes. Based on 100 parts of cement, 80-120 mesh quartz sand (particle size 0.125-0.18mm) is 50 parts, 40-70 mesh (particle size 0.212-0.425mm) is 42 parts, 20-40 mesh (particle size 0.425-0.85mm) is 50 parts, and 10-20 mesh (particle size 0.85-2.00mm) is 7 parts. The sand-cement ratio is 1.1.

[0074] The coarse aggregate is basalt crushed stone with a particle size of 5-10mm and a mud content of ≤0.5%. Based on 100 parts of cement, the coarse aggregate of basalt crushed stone is 32 parts.

[0075] The steel fiber is a copper-plated steel fiber with a length of 14 mm, a diameter of 0.2 mm, a straight type, and a tensile strength of ≥2000 MPa, and is added at a volume ratio of 2%, that is, 160 kg of steel fiber per cubic meter.

[0076] The water reducer used is the 3301 polycarboxylic acid water reducer produced by Sika Company, with a water reduction rate of ≥30% and a solid content of 40%.

[0077] The water-to-cement ratio is 0.2.

[0078] A method for preparing ultra-high performance concrete is as follows:

[0079] First, dry mix the fine aggregate and cementitious materials, cement, silica fume, and fly ash in a mortar mixing pot for 1 minute.

[0080] Then, mix the water and water reducer evenly and pour them into the mixing container to start wet mixing. After the UHPC mortar becomes fluid after 2-3 minutes, continue stirring for 5-6 minutes.

[0081] Finally, steel fiber and coarse aggregate were added and stirred for 5 minutes to obtain an ultra-high performance concrete mixture.

[0082] A curing method for ultra-high performance concrete is as follows:

[0083] First, the ultra-high performance concrete is cast and formed, vibrated on a vibrating table for 5-10 seconds, and then covered with a curing film and placed in a standard curing room;

[0084] Then, the mold is removed after one day of curing, and the curing is continued until the strength test is carried out after 28 days. The curing temperature is 20±2℃ and the relative humidity is above 95%, which is standard curing.

[0085] Example 2

[0086] This embodiment 2 provides an ultra-high performance concrete configuration scheme, which differs from embodiment 1 in that the basalt crushed stone coarse aggregate is eliminated, the maximum aggregate size in the mix design is 2.0 mm, and the water-cement ratio is reduced to 0.19.

[0087] Example 3

[0088] This embodiment 3 provides an ultra-high performance concrete configuration scheme, which differs from embodiment 2 in that the water-cement ratio is reduced to 0.18.

[0089] Comparative Examples 1-3

[0090] Comparative Examples 1-3 provide an ultra-high performance concrete configuration scheme, which differs from Example 2 in that the particle size and gradation of quartz sand are changed. The specific scheme is detailed in Table 1.

[0091] Comparative Example 4

[0092] This Example 4 provides an ultra-high performance concrete configuration scheme, which differs from Example 2 in that it uses fully densified silica fume.

[0093] Comparative Example 5

[0094] This Example 5 provides an ultra-high performance concrete configuration scheme, which differs from Example 2 in that the amount of mineral admixtures is reduced. Specifically, the amount of silica fume is 12.5% ​​of the cement amount, and the amount of fly ash is 8% of the cement amount.

[0095] Comparative Example 6

[0096] This ratio 6 provides an ultra-high performance concrete configuration scheme, which differs from Example 2 in that the silica fume content is increased and the fly ash content is reduced on the basis of keeping the total amount of mineral admixtures unchanged. Specifically, the silica fume content is 30% of the cement content, and the fly ash content is 5% of the cement content.

[0097] Comparative Example 7

[0098] This Example 7 provides an ultra-high performance concrete configuration scheme, which differs from Example 2 in that fly ash is used instead of Class F Grade I fly ash.

[0099] The above embodiments and comparative examples all adopted the same stirring process and curing standards.

[0100] Table 1 lists the raw materials and configurations of each embodiment and comparative example (by weight fraction)

[0101]

[0102]

[0103] Working performance and strength test

[0104] According to the method specified in GB / T 17671-2021, Test Method for Cement Mortar Strength (ISO Method), the compressive strength of the ultra-high performance concrete test blocks in each embodiment and comparative example was tested, and the test results are shown in Table 2. According to the method specified in GB / T 50080-2016, the working performance of the ultra-high performance concrete in each embodiment and comparative example was tested, and the test results are shown in Table 2.

[0105] Table 2 Performance test results

[0106]

[0107] From the results in Table 2, it can be seen that in Example 1, by adding 23 parts of semi-densified silica fume and 13 parts of Class F Grade I fly ash to improve the flowability and later strength, and introducing 50 parts of large-particle quartz sand with a particle size of 10-20 mesh and 50 parts of basalt crushed stone with a particle size of 5-10mm, the compressive strength can reach 188MPa after only 28 days of standard curing. Unlike the destruction mode of ordinary concrete, ultra-high performance concrete has no obvious debris during compressive destruction, has strong integrity and is accompanied by an explosion sound. Observation of the destruction section shows that the basalt coarse aggregate is crushed and sheared, indicating that the interface between the matrix and the coarse aggregate is well bonded. The addition of semi-densified silica fume improves the transition zone of the coarse aggregate interface and improves the strength. The ultra-high performance concrete described in Example 1 uses only 648kg / m 3 At the same time, the expansion reaches 660cm, meeting the construction work requirements.

[0108] In Example 2, compared to Example 1, the 5-10 mm basalt crushed stone was eliminated. The quartz sand particle size and gradation remained the same as in Example 1. The water-binder ratio was reduced from 0.20 to 0.19 to improve strength. Tests revealed that the material's expansion significantly increased to 750 mm, while its compressive strength decreased slightly to 185 MPa. In Example 3, the water-binder ratio was further reduced to 0.18, further increasing its strength to 189 MPa and achieving an expansion of 704 mm.

[0109] Examples 1-3 are based on P.O42.5 ordinary Portland cement, the expansion degrees all meet the construction requirements, and the strengths are all above 185 MPa. In particular, by introducing larger particle size basalt gravel in Example 1, the cement dosage can be further reduced and the material elastic modulus can be increased, making it suitable for large-scale lightweight main engineering structure applications.

[0110] Comparative Examples 1-3 gradually reduce the content of large-particle quartz sand compared to the embodiment. The test found that the fluidity is improved, but the strength is significantly reduced due to the weakening of the aggregate effect of the fine aggregate of quartz sand. The compressive strength of Comparative Examples 1-3 is reduced by 7.6%, 13.5%, and 15.1% respectively compared to Example 2, which is difficult to meet the high strength requirements. The present invention can be concluded that the large-particle aggregate skeleton can be fully utilized to improve the strength and elastic modulus of ultra-high performance concrete without increasing the cement grade, steel fiber dosage and maintenance standards, and reduce material shrinkage, which is beneficial to on-site production and material promotion.

[0111] Comparative Example 4 uses fully densified silica fume to replace the semi-densified silica fume in Example 2, and the compressive strength decreases slightly. However, since the fully densified silica fume particles are larger, they cannot fill the gaps between cement particles to reduce water demand. At the same time, it takes 10 minutes for the slurry to begin to flow during the stirring process, and the expansion degree is significantly reduced, which is difficult to apply to actual projects.

[0112] Comparative Example 5 reduces the amount of mineral admixtures in the ultra-high performance concrete system, increases the amount of cement, and at the same time slightly decreases the compressive strength and expansion.

[0113] In Comparative Example 6, while keeping the total amount of mineral admixtures in the ultra-high performance concrete system unchanged, the amount of silica fume added was increased and the amount of fly ash added was reduced. Due to the large specific surface area of ​​silica fume, the water demand increased when it was over-added, resulting in a decrease in expansion, while also increasing the construction cost.

[0114] In Comparative Example 7, in order to improve fluidity, microspheres were used instead of Class F Grade I fly ash to give full play to the ball effect of the fly ash microspheres to reduce the viscosity of the slurry. The test found that due to the hollow structure of the microsphere particles, the compressive strength was significantly reduced, and the fly ash microspheres were difficult to be used in the ultra-high performance concrete described in the present invention.

[0115] 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 present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications based on the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

[0116] The endpoints and any values ​​of the ranges 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 endpoint values ​​of each range, the endpoint values ​​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 as specifically disclosed herein.

Claims

1. A non-autoclaved UHPC with low cement content based on P.O.42.5, characterized by: Ultra-high performance concrete includes the following components by weight: 100 parts of cement, 13-30 parts of silica fume, 5-13 parts fly ash, 149-181 parts of quartz sand and coarse aggregate, 18-23 parts of steel fiber, 2 parts of water reducing agent, 22-26 parts water.

2. The autoclaved UHPC with low cement content based on P.O.42.5 according to claim 1, characterized in that: The cement, silica fume and fly ash constitute the cementitious material.

3. The autoclaved UHPC with low cement content based on P.O.42.5 according to claim 2, characterized in that: The cement in the cementitious material is P.O42.5 Jinyu Jidong ordinary Portland cement, and the storage period is no more than 3 months.

4. The autoclaved UHPC with low cement content based on P.O.42.5 according to claim 2, characterized in that: The silica fume in the cementitious material is semi-densified silica fume, the mass of which accounts for 15%-30% of the total mass of the cementitious material, and the density is 300kg / m 3 , particle size is 0.1-2μm.

5. The autoclaved UHPC with low cement content based on P.O.42.5 according to claim 2, characterized in that: The fly ash in the cementitious material is Class F Grade I fly ash, the mass of the fly ash accounts for 5%-12.5% ​​of the total mass of the cementitious material, and the main particle size is 1-100 μm.

6. The autoclaved UHPC with low cement content based on P.O.42.5 according to claim 1, characterized in that: The quartz sand and the quartz sand in the coarse aggregate are refined quartz sand, and the SiO2 content thereof is above 98%.

7. The autoclaved UHPC with low cement content based on P.O.42.5 according to claim 1, characterized in that: The quartz sand and coarse aggregate are made of basalt crushed stone with a particle size of 5-10mm and a mud content of ≤0.5%; The quartz sand is refined quartz sand, which is divided into four mesh sizes: 80~120 mesh (particle size 0.125~0.18 mm), 40~70 mesh (particle size 0.212~0.425mm), 20~40 mesh (particle size 0.425~0.85 mm), 10~20 mesh (particle size 0.85~2.00mm).

8. The autoclaved UHPC with low cement content based on P.O.42.5 according to claim 1, characterized in that: The steel fiber is a straight copper-plated steel fiber with a length of 14 mm and a diameter of 0.2 mm, and its tensile strength is ≥2000 MPa.

9. The method for preparing autoclaved UHPC with low cement content and P.O.42.5 according to claim 1, characterized in that: The following steps are involved: First, fine aggregate and cementitious materials, namely cement, silica fume and fly ash, were dry-mixed in a mortar mixing pot for 1 minute. Then, mix the water and water reducer evenly and pour into the mixing container to start wet mixing; After that, after 2-3 minutes, when the ultra-high performance concrete mortar becomes fluid, continue stirring for 5-6 minutes; Finally, steel fibers and coarse aggregates were added and stirred for 5 minutes to uniformly disperse the steel fibers and coarse aggregates to obtain an ultra-high performance concrete mixture.

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