High-performance concrete and preparation method thereof

Abstract

According to the high-performance concrete and the preparation method thereof, machine-made sand, steel fibers and PVA fibers are modified, the machine-made sand is activated through water vapor, micro-cracks in the surface of the machine-made sand are opened, PVA-g-SiO2 is sprayed on the machine-made sand through high-speed airflow to form an anchor structure, and the anchor structure can improve the binding force with the PVA fibers and the steel fibers, so that the strength of the machine-made sand is improved; the bonding force of fine aggregate to fibers is improved, the fibers are protected, PVA fibers are modified through silane, the stress defect caused by damage of the PVA fibers in concrete is avoided, the slump of the concrete can be improved through the modified PVA fibers, the dispersion index of the fibers can be increased, the initial crack strength of the concrete can be improved, and the strength of the concrete can be improved through passivation rust-proof treatment on the steel fibers. The durability of the concrete is enhanced; the compressive strength of the concrete is improved; the diffusion coefficient of chloride ions of the concrete is reduced; the weather resistance is improved.

Description

Technical Field

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

[0002] Concrete is a basic material widely used in the construction field, especially high-performance concrete, which is of great significance as an important building material.

[0003] CN114315278B discloses a high-density rubberized high-performance concrete and its preparation method. The concrete comprises the following raw materials and their weight proportions: cement: 390-450 parts; mineral powder: 50-100 parts; high-density rubber particles: 20-60 parts; sand: 500-750 parts; crushed stone: 1000-1100 parts; water reducer: 4-5 parts; mixing water: 145-155 parts. The preparation method comprises: weighing high-density rubber particles, cement, mineral powder, sand, crushed stone, water reducer, and mixing water according to a predetermined mix ratio, placing them in a concrete mixer and stirring them uniformly to obtain high-density rubberized concrete. However, due to the use of rubber for modification, the concrete has insufficient compressive strength. Furthermore, the concrete is prepared using natural sand, which does not meet the demand for replacing manufactured sand.

[0004] For example, Chinese invention patent CN107913777A discloses a dry-process process for producing machine-made sand using tailings sand as the primary raw material. This process uses tailings sand with a particle size of less than 5 mm, which can be mixed with 0-50% gravel larger than 5 mm. The tailings sand is then processed into qualified machine-made sand through a series of steps: desludging, separation of fine sand, coarse sand, and gravel, crushing of the coarse sand and gravel, de-powdering of the fine sand, and mixing and humidifying the coarse and fine sand. However, this dry-process is complex, has high processing costs, and is difficult to control stone dust.

[0005] Chinese invention patent CN116333507B discloses an ultra-tough, high-strength wearing layer of asphalt concrete doped with steel slag and its preparation. The components, by weight, include: 30-60 parts resin; 10-20 parts steel slag; 15-35 parts toughening agent; 10-40 parts curing agent; and 155-185 parts asphalt. A weight ratio of steel slag to asphalt of 1:(10-20) can improve the toughness and tensile strength of the wearing layer. Component 1 has an average particle size of 4.75-9.5 mm, which can improve the water resistance of the wearing layer. Aging for 12-24 months can improve the tensile strength of the wearing layer. However, this concrete suffers from unstable quality, and steel slag, as a key modifier, has uncertain composition.

[0006] Based on the above defects, the inventors proposed a high-performance concrete and its preparation method, aiming to solve the technical problems of poor fiber matching caused by the defects of artificial sand itself when artificial sand replaces natural sand in high-performance concrete in the existing technology, such as insufficient bond strength, fiber damage and poor fiber dispersion. Summary of the Invention

[0007] The object of the present invention is to provide a high performance concrete and a preparation method thereof to solve the problems existing in the above background.

[0008] In the first aspect, the present invention provides a high performance concrete comprising the following raw materials: cement 480-520 kg / m 3 , first-grade fly ash 80-100kg / m 3 , machine-made sand 550-650kg / m 3 , coarse aggregate 950-1200kg / m 3 , water reducing agent 8-10kg / m 3 , water 180-200kg / m 3 , steel fiber 60-90kg / m 3 , PVA fiber 2-10kg / m 3 ;

[0009] Preferably, the machine-made sand is modified by the following steps: the machine-made sand is activated by saturated water vapor at 0.1-0.3 MPa for 0.5-1 hour, sprayed with PVA-g-SiO2 to form modified machine-made sand, then soaked in 3-5wt% oxalic acid solution for 10-15 minutes, and dried and solidified with hot air at 60-80°C;

[0010] Preferably, the PVA-g-SiO2 is prepared by the following means:

[0011] SiO2 with an average diameter of 50-150 nm is dispersed in a solution of 1:1 ethanol:water; 1-3 wt% of a coupling agent is added, and the mixture is refluxed at 60-90°C for 5-8 hours to obtain amino-SiO2;

[0012] Take a 10 wt% PVA aqueous solution with an alcoholysis degree greater than 99%, heat it to 80-90°C to dissolve it, add Na1O4, and react at 50-60°C for 1-2 hours to obtain oxidized PVA;

[0013] Add amination SiO2 to oxidized PVA, adjust the pH value to 5.0-6.0 with a buffer solution, and react for 6-12 hours to obtain PVA-g-SiO2.

[0014] Preferably, the gas pressure for spraying PVA-g-SiO2 is 0.6-0.8 MPa.

[0015] Preferably, the PVA fibers are treated by silane impregnation.

[0016] The PVA limit has the following parameters:

[0017]

[0018] Preferably, the PVA fiber is immersed in a mixed solution of 5 wt% heptafluorodecyltrimethoxysilane + ethanol: water (4:1) + 0.1 mol / L acetic acid solution for 30-60 seconds and then irradiated to obtain the modified PVA fiber.

[0019] Preferably, the steel fiber has a diameter of 0.2 mm, a length of 5-12 mm, and an aspect ratio of 25-60.

[0020] Preferably, the steel fiber also has the following basic physical parameters:

[0021]

[0022] Preferably, the first-level fly ash has a fineness of 8.0, a water requirement of 80, a loss on ignition of 2.0, a sulfur trioxide content of 1.5, a 7d activity index of 75, and a 28d activity index of 85.

[0023] Preferably, the raw material of the machine-made sand is granite or quartz stone.

[0024] In a second aspect, the present application also provides a method for preparing high performance concrete, comprising the following steps:

[0025] Preferably, the raw materials include: cement 480-520kg / m 3 , first-grade fly ash 80-100kg / m 3 , machine-made sand 550-650kg / m 3 , coarse aggregate 950-1200kg / m 3 , water reducing agent 8-10kg / m 3 , water 180-200kg / m 3 , steel fiber 60-90kg / m 3 , PVA fiber 2-10kg / m 3 ;

[0026] Step 1, modifying fine aggregate and steel fiber;

[0027] Step 2: Add coarse aggregate, fine aggregate and modified steel fiber according to the raw material ratio and dry mix;

[0028] Step 3, adding cement and fly ash and continuing dry mixing;

[0029] Step 4: Add evenly dispersed water and water reducing agent, stir and disperse until a concrete matrix is ​​formed;

[0030] Step 5, modifying the PVA fibers, dispersing the modified PVA fibers and adding them to the concrete matrix, and continuously stirring;

[0031] Step 6: Take the concrete mixed evenly in step 5, continuously vibrate it, and then put it into the mold, cure it, and test it.

[0032] Preferably, the modification method of the fine aggregate is as follows:

[0033] Step 1: Activate the machine-made sand with saturated steam at 0.1-0.3 MPa for 0.5-1 hour;

[0034] Step 2, spraying PVA-g-SiO2 to form modified machine-made sand;

[0035] The PVA-g-SiO2 is prepared by the following means:

[0036] SiO2 with an average diameter of 50-150 nm is dispersed in a solution of 1:1 ethanol:water; 1-3 wt% of a coupling agent is added, and the mixture is refluxed at 60-90°C for 5-8 hours to obtain amino-SiO2;

[0037] Take a 10 wt% PVA aqueous solution with an alcoholysis degree greater than 99%, heat it to 80-90°C to dissolve it, add Na1O4, and react at 50-60°C for 1-2 hours to obtain oxidized PVA;

[0038] Adding aminated SiO2 to oxidized PVA, adjusting the pH to 5.0-6.0 with a buffer solution, and reacting for 6-12 hours to obtain PVA-g-SiO2;

[0039] Step 3, soaking the modified machine-made sand in step 2 for 10-15 minutes with 3-5wt% oxalic acid solution;

[0040] Step 4: Dry and solidify with hot air at 60-80°C to obtain modified fine aggregate machine-made sand.

[0041] Preferably, the steel fiber is modified by the following method:

[0042] Step 1: Cleaning the steel fiber by soaking it in 3-5wt% NaOH + 2-3wt% Na2CO3 + 0.1-0.3wt% non-ionic surfactant and drying it at 50-60°C;

[0043] Step 2, activating the steel fiber with 2-8% vol% H2SO4 + 0.5wt% thiourea and washing with water until neutral;

[0044] Step 3, passivating the steel fiber with a passivation solution formed by sodium molybdate, chromic anhydride, zinc dihydrogen phosphate, H3PO4, and polyaspartic acid, and drying with hot air;

[0045] Preferably, the concentration of sodium molybdate (Na2MoO4) is 10-15 g / L, chromic anhydride (CrO3) is 0.1-0.3 g / L, and zinc dihydrogen phosphate (Zn(H2Po4)2) is 2-5 g / L; phosphoric acid is used to adjust the pH value to 3-4, and the concentration of polyaspartic acid (PASP) is 0.2-0.5 g / L.

[0046] Step 4: soaking the steel fiber obtained in step 3 with 3 wt % silane coupling agent KH-560.

[0047] The nonionic surfactant is Tween series, such as Tween 80.

[0048] Preferably, the PVA fiber is immersed in a mixed solution of 5 wt% heptafluorodecyltrimethoxysilane + ethanol: water (4:1) + 0.1 mol / L acetic acid solution for 30-60 seconds and then irradiated to obtain the modified PVA fiber.

[0049] Beneficial effects of the present invention:

[0050] (1) The present invention activates machine-made sand by water vapor, opens microcracks on the surface of the machine-made sand, and sprays PVA-g-SiO2 by high-speed airflow to form an anchor structure on the machine-made sand. The anchor structure can improve the bonding strength with PVA fibers and steel fibers, improve the grip of fine aggregate on the fibers, and protect the fibers.

[0051] (2) By spraying PVA-g-SiO2 grafted concrete materials on machine-made sand, the durability data in alkaline environment can be improved, as well as the cost advantage compared with traditional coatings such as epoxy resin.

[0052] (3) By modifying PVA fibers and modifying PVA fibers with silane, the PVA fibers can be prevented from being damaged in concrete and causing stress defects. By modifying PVA fibers, the slump of concrete can be increased, the dispersion index of the fibers can be increased, and the initial crack strength of concrete can be increased.

[0053] (4) Through the passivation and rust prevention treatment of steel fibers, the weather resistance of concrete is improved, the durability of concrete is enhanced, the compressive strength of concrete is improved, the diffusion coefficient of chloride ions in concrete is reduced, and the freeze-thaw quality loss of concrete is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Specimen loading device;

[0055] Figure 2 Schematic diagram of strain gauge and linear displacement meter;

[0056] Figure 3 Schematic diagram of specimen crushing. DETAILED DESCRIPTION

[0057] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0058] Example 1

[0059] A high performance concrete comprising the following raw materials: cement 480kg / m 3 , first-grade fly ash 80kg / m 3 , machine-made sand 550kg / m 3 , coarse aggregate 950kg / m 3 , water reducing agent 8kg / m 3 , water 180kg / m 3 , steel fiber 60kg / m 3 , PVA fiber 2kg / m 3 ;

[0060] Specifically, the machine-made sand is modified by the following steps: the machine-made sand is activated by 0.3 MPa saturated water vapor for 0.5 hours, sprayed with PVA-g-SiO2 to form modified machine-made sand, then soaked in 5 wt% oxalic acid solution for 10 minutes, and dried and solidified with hot air at 60°C. The PVA-g-SiO2 is prepared by the following means:

[0061] SiO2 with an average diameter of 50 nm was dispersed in a solution of 1:1 ethanol:water;

[0062] Add 1-3 wt% of coupling agent KH550 and reflux at 60°C for 5 hours to obtain amination SiO2;

[0063] A 10 wt% PVA aqueous solution with an alcoholysis degree greater than 99% was heated to 80°C to dissolve, and Na1O4 was added and reacted at 50°C for 1 hour to obtain oxidized PVA;

[0064] Amination of SiO2 was added to oxidized PVA, the pH value was adjusted to 5.0 with a buffer solution, and the reaction was carried out for 6 hours to obtain PVA-g-SiO2.

[0065] The air pressure for spraying PVA-g-Sio2 is 0.6 MPa.

[0066] The PVA fiber is treated by silane impregnation; the PVA fiber is immersed in a mixed solution of 5wt% heptafluorodecyltrimethoxysilane + ethanol: water (4:1) + 0.1mol / L acetic acid solution for 30-60 seconds and then irradiated to obtain the modified PVA fiber.

[0067] The steel fiber has a diameter of 0.2 mm, a length of 12 mm, and an aspect ratio of 60.

[0068] The first-grade fly ash has a fineness of 8.0, a water requirement of 80, a loss on ignition of 2.0, a sulfur trioxide content of 1.5, a 7d activity index of 75, and a 28d activity index of 85.

[0069] The raw material of the machine-made sand is granite.

[0070] The method for preparing the high performance concrete is characterized by comprising the following steps:

[0071] Step 1, modifying fine aggregate and steel fiber;

[0072] Step 2: Add coarse aggregate, fine aggregate and modified steel fiber according to the raw material ratio and dry mix;

[0073] Step 3, adding cement and fly ash and continuing dry mixing;

[0074] Step 4: Add evenly dispersed water and water reducing agent, stir and disperse until a concrete matrix is ​​formed;

[0075] Step 5: Modify the PVA fibers, disperse the modified PVA fibers into the concrete matrix, and continue stirring;

[0076] Step 6: Take the concrete mixed evenly in step 5, continuously vibrate it, and then put it into the mold, cure it, and test it.

[0077] The steel fiber is modified by the following method:

[0078] Step 1: Cleaning the steel fiber by soaking it in 3wt% NaOH+2wt% Na2Co3+0.1wt% non-ionic surfactant and drying it at 50°C;

[0079] Step 2: activating the steel fiber with 2 vol% H2SO4+0.5 wt% thiourea and washing with water until neutral;

[0080] Step 3: Passivate the steel fiber with a passivation solution formed by sodium molybdate, chromic anhydride, zinc dihydrogen phosphate, H3Po4, and polyaspartic acid, and then dry it with hot air; the concentration of sodium molybdate (Na2Moo4) is 10g / L, chromic anhydride (CrO3) is 0.3g / L, and zinc dihydrogen phosphate (Zn(H2PO4)2) is 5g / L; phosphoric acid is used to adjust the pH value to 3, and the concentration of polyaspartic acid (PASP) is 0.2g / L.

[0081] Step 4: soaking the steel fiber obtained in step 3 with 3 wt % silane coupling agent KH-560.

[0082] The PVA fibers are soaked in a mixed solution of 5wt% heptadecyltrimethoxysilane, ethanol:water (4:1) and 0.1mol / L acetic acid solution for 30-60 seconds and then irradiated to obtain modified PVA fibers.

[0083] In order to study the mechanical properties of machine-made sand high-performance concrete under axial compression, the present invention combines domestic and foreign standards, prepares three cylindrical specimens with a diameter of 150 mm and a height of 300 mm for each concrete mix ratio, and uses a MATESTC088-01 testing machine. Figure 1 As shown in Figure 1, the maximum loading capacity of the equipment is 4000 kN. This test follows the US standard and, in order to obtain a more complete stress-strain curve, the loading speed is set to 0.18 mm / min.

[0084] Before testing, to prevent bias from affecting test accuracy, the upper and lower ends of the specimen should be plastered and leveled. Once leveled, strain gauges can be attached. Two longitudinal and one transverse strain gauges should be symmetrically attached at a height of 150 mm, between 100 and 200 mm, to measure the specimen's longitudinal and transverse strains. The resistance and sensitivity of the four strain gauges are 120 ± 0.1 Ω and 2.08 ± 1%, respectively. The sensitive grid lengths of the longitudinal and transverse strain gauges are 100 mm and 80 mm, respectively.

[0085] Before starting the test loading, the hoop is used to fix the specimen. At the same time, the linear displacement meter is placed opposite to the longitudinal strain gauge, such as Figure 2 As shown. Furthermore, to prevent the influence of bias on the test results, the concrete should be preloaded, and the data from the two longitudinal strain gauges should be compared for similarity. This ensures a close fit between the loading surface of the testing machine and the end of the specimen, thereby improving test accuracy. The specimen's axial stress σ and axial strain ε can be calculated using Equations 1 and 2.

[0086]

[0087] Where F refers to the applied load; A refers to the cross-sectional area of ​​the specimen; and s refers to the displacement measured by the linear displacement meter.

[0088] Example 2

[0089] Compared with Example 1, the difference is that the amount of steel fiber added is 65kg / m 3 , PVA fiber 4kg / m 3 .

[0090] Example 3

[0091] Compared with Example 1, the difference is that the amount of steel fiber added is 70kg / m 3 , PVA fiber 6kg / m 3 .

[0092] Example 4

[0093] Compared with Example 1, the difference is that the amount of steel fiber added is 70kg / m 3 , PVA fiber 8kg / m 3 .

[0094] Example 5

[0095] Compared with Example 1, the difference is that the amount of steel fiber added is 70kg / m 3 , PVA fiber 10kg / m 3 .

[0096] Comparative Example 1

[0097] Compared with Example 1, the comparative example did not modify the machine-made sand, steel fiber, or PVA fiber.

[0098] A high performance concrete comprising the following raw materials: cement 480kg / m 3 , first-grade fly ash 80kg / m 3 , machine-made sand 550kg / m 3 , coarse aggregate 950kg / m 3 , water reducing agent 8kg / m 3 , water 180kg / m 3 , steel fiber 60kg / m 3 , PVA fiber 2kg / m 3 ;

[0099] The steel fiber has a diameter of 0.2 mm, a length of 12 mm, and an aspect ratio of 60.

[0100] The first-grade fly ash has a fineness of 8.0, a water requirement of 80, a loss on ignition of 2.0, a sulfur trioxide content of 1.5, a 7d activity index of 75, and a 28d activity index of 85.

[0101] The raw material of the machine-made sand is granite.

[0102] The method for preparing the high performance concrete is characterized by comprising the following steps:

[0103] Step 1: Add coarse aggregate, fine aggregate and steel fiber according to the raw material ratio and dry mix;

[0104] Step 2, adding cement and fly ash and continuing dry mixing;

[0105] Step 3, adding evenly dispersed water and water reducing agent, stirring and dispersing until a concrete matrix is ​​formed;

[0106] Step 4: PVA fibers are dispersed and added into the concrete matrix with continuous stirring;

[0107] Step 5: Take the concrete mixed evenly in step 4, continuously vibrate it, and then put it into a mold for curing and testing.

[0108] Comparative Example 2

[0109] Compared with Example 1, Comparative Example 2 did not modify the manufactured sand, and the rest was the same.

[0110] Comparative Example 3

[0111] Compared with Example 1, Comparative Example 3 did not modify the machine-made sand and steel fiber, and the rest was the same.

[0112] Comparative Example 4

[0113] Compared with Example 1, Comparative Example 4 did not modify the machine-made sand and PVA fiber, and the rest was the same.

[0114] Testing the slump of high performance concrete.

[0115] The test results are shown in Table 1.

[0116]

[0117]

[0118] The present invention improves the 28d compressive strength of concrete by modifying fine aggregate machine-made sand, steel fiber and PVA fiber, maintains a good elastic modulus, and improves the fluidity of concrete, which has a synergistic effect. The high-performance concrete after modification can significantly improve the weather resistance of concrete and make the concrete resistant to marine engineering environments.

[0119] Although not fully specified, the compressive strength, elastic modulus, slump, and 90d chloride ion diffusion coefficient in the present invention are all tested using known testing methods.

[0120] The above is a detailed introduction to a modified machine-made sand and a preparation method thereof provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enables any technician in this field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method.

[0121] It should be noted that those skilled in the art will readily appreciate that various improvements and modifications may be made to the present invention without departing from the principles of the present invention. In particular, as long as no structural conflicts exist, the various features of the embodiments disclosed herein may be combined with one another in any manner. The omission of an exhaustive description of these combinations in this specification is solely for the sake of space and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A high performance concrete comprising the following raw materials: cement 480-520 kg / m 3 , first-grade fly ash 80-100kg / m 3 , machine-made sand 550-650kg / m 3 , coarse aggregate 950-1200kg / m 3 , water reducing agent 8-10kg / m 3 , water 180-200kg / m 3 , steel fiber 60-90kg / m 3 , PVA fiber 2-10kg / m 3 It is characterized in that the machine-made sand is modified by the following steps: the machine-made sand is activated by saturated water vapor of 0.1-0.3MPa for 0.5-1 hour, PVA-g-SiO2 is sprayed to form modified machine-made sand, and then it is soaked in 5% oxalic acid solution for 10-15 minutes, and dried and solidified with hot air at 60-80°C. The PVA-g-SiO2 is prepared by the following means: SiO2 with an average diameter of 50-150 nm is dispersed in a solution of 1:1 ethanol:water; 1-3 wt% of a coupling agent is added, and the mixture is refluxed at 60-90°C for 5-8 hours to obtain amino-SiO2; Take a 10 wt% PVA aqueous solution with an alcoholysis degree greater than 99%, heat it to 80-90°C to dissolve it, add Na1O4, and react at 50-60°C for 1-2 hours to obtain oxidized PVA; Add amination SiO2 to oxidized PVA, adjust the pH value to 5.0-6.0 with a buffer solution, and react for 6-12 hours to obtain PVA-g-SiO2.

2. The high performance concrete according to claim 1, characterized in that: The gas pressure for spraying PVA-g-SiO2 is 0.6-0.8 MPa.

3. The high performance concrete according to claim 1, characterized in that: The PVA fibers are treated by silane impregnation.

4. The high performance concrete according to claim 1, characterized in that: The steel fiber has a diameter of 0.2 mm, a length of 5-12 mm, and an aspect ratio of 25-60.

5. The high performance concrete according to claim 1, characterized in that: The first-grade fly ash has a fineness of 8.0, a water requirement of 80, a loss on ignition of 2.0, a sulfur trioxide content of 1.5, a 7d activity index of 75, and a 28d activity index of 85.

6. The high performance concrete according to claim 1, characterized in that: The raw material of the machine-made sand is granite or quartz stone.

7. A method for preparing high performance concrete according to claims 1 to 6, characterized in that The steps include: Step 1, modifying fine aggregate and steel fiber; Step 2: Add coarse aggregate, fine aggregate and modified steel fiber according to the raw material ratio and dry mix; Step 3, adding cement and fly ash and continuing dry mixing; Step 4: Add evenly dispersed water and water reducing agent, stir and disperse until a concrete matrix is ​​formed; Step 5: Modify the PVA fibers, disperse the modified PVA fibers into the concrete matrix, and continue stirring; Step 6: Take the concrete mixed evenly in step 5, continuously vibrate it, and then put it into the mold, cure it, and test it.

8. A method for preparing high performance concrete according to claim 7, characterized in that: The modification method of the fine aggregate is as follows: Step 1: Activate the machine-made sand with saturated steam at 0.1-0.3 MPa for 0.5-1 hour; Step 2, spraying PVA-g-Sio2 to form modified machine-made sand; The PVA-g-Sio2 is prepared by the following means: SiO2 with an average diameter of 50-150 nm is dispersed in a solution of 1:1 ethanol:water; 1-3 wt% of a coupling agent is added, and the mixture is refluxed at 60-90°C for 5-8 hours to obtain amino-SiO2; Take a 10 wt% PVA aqueous solution with an alcoholysis degree greater than 99%, heat it to 80-90°C to dissolve it, add Nalo4, and react at 50-60°C for 1-2 hours to obtain oxidized PVA; Adding aminated SiO2 to oxidized PVA, adjusting the pH to 5.0-6.0 with a buffer solution, and reacting for 6-12 hours to obtain PVA-g-SiO2; Step 3: soak the modified machine-made sand in step 2 with 5% oxalic acid solution for 10-15 minutes; Step 4: Dry and solidify with hot air at 60-80°C to obtain modified fine aggregate machine-made sand.

9. A method for preparing high performance concrete according to claim 7, characterized in that: The steel fiber is modified by the following method: Step 1: Cleaning the steel fiber by soaking it in 3-5wt% NaOH + 2-3wt% Na2CO3 + 0.1-0.3wt% non-ionic surfactant and drying it at 50-60°C; Step 2, activating the steel fiber with 2-8% vol% H2SO4 + 0.5wt% thiourea and washing with water until neutral; Step 3, passivating the steel fiber with a passivation solution formed by sodium molybdate, chromic anhydride, zinc dihydrogen phosphate, H3Po4, and polyaspartic acid, and drying with hot air; Step 4: soaking the steel fiber obtained in step 3 with 3 wt % silane coupling agent KH-560.

10. A method for preparing high performance concrete according to any one of claims 7 to 9, characterized in that: The PVA fiber is immersed in a mixed solution of 5wt% heptafluorodecyltrimethoxysilane + ethanol: water (4:1) + 0.1mol / L acetic acid solution for 30-60 seconds and then irradiated to obtain the modified PVA fiber.

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