Ultra-high performance fiber-reinforced concrete and its preparation method

Abstract

This invention discloses an ultra-high performance fiber-reinforced concrete and its preparation method, mainly composed of the following raw materials in parts by weight: 60-65 parts cement, 15-36 parts silica fume, 20-50 parts fly ash, 20-25 parts quartz powder, 45-55 parts quartz sand, 4-8 parts mixed fibers, 1-2 parts water-reducing agent, and 20-100 parts water; the mixed fibers are mainly composed of 2-4 parts basalt fiber, 1-2 parts PVA fiber, and 1-2 parts PE fiber; the basalt fiber is a mixture of basalt fibers of different lengths. The ultra-high performance fiber-reinforced concrete provided by this invention possesses excellent mechanical properties and can be used for long-term applications in high-speed rail cable troughs and covers, pedestrian bridges, lightweight bridge decks, low-ribbed composite beams, steel arch bridges, building exterior finishes, and repair and reinforcement structures.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to an ultra-high performance fiber-reinforced concrete and its preparation method. Background Technology

[0002] Ultra-high performance fiber-reinforced concrete (UHVFC), also known as reactive powder concrete, is one of the most promising cement-based fiber-reinforced composite materials available today. UHVFC features a densely packed mortar matrix forcibly reinforced by randomly distributed high-strength chopped steel fibers, exhibiting strain-hardening behavior accompanied by repeated cracking. The mortar matrix typically comprises cement, fine sand (average size <0.5 mm), silica fume or silica fume, a superplasticizer, and water with a low water / binder ratio. Coarse aggregates are not used in the preparation of UHVFC to ensure uniform fiber dispersion and maximum bulk density. This type of UHVFC exhibits higher tensile strength, compressive strength, fracture energy, ductility, and durability than conventional strength concrete and high-performance concrete. However, the potential of this material remains largely untapped in engineering practice, primarily due to its significantly higher cost compared to other concrete products. Therefore, optimizing the material, fiber dosage, and blending effects to reduce the cost of UHVFC is crucial for its future development and application.

[0003] Existing literature CN 107721317 A discloses a method for preparing basalt and polyvinyl alcohol (PVA) hybrid fiber concrete, wherein the hybrid fiber is a hybrid fiber composed of low-dosage basalt fiber and PVA fiber. However, the overall compressive strength and flexural strength of the concrete are difficult to meet the performance requirements of ultra-high performance fiber reinforced concrete, and this concrete is not suitable for extreme environments.

[0004] Therefore, it is extremely urgent to develop an ultra-high performance fiber-reinforced concrete suitable for extremely harsh environments. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an ultra-high performance fiber-reinforced concrete and its preparation method.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] The first aspect of this invention provides an ultra-high performance fiber-reinforced concrete, which is mainly prepared from the following raw materials in parts by weight: 60-65 parts cement, 15-36 parts silica fume, 20-50 parts fly ash, 20-25 parts quartz powder, 45-55 parts quartz sand, 4-8 parts mixed fibers, 1-2 parts water-reducing agent, and 20-100 parts water.

[0008] Preferably, the hybrid fiber is mainly composed of basalt fiber, PVA fiber and ultra-high molecular weight polyethylene (PE) fiber.

[0009] More preferably, the basalt fiber is first modified to obtain modified basalt fiber, and then the modified basalt fiber is mixed with PVA fiber and PE fiber.

[0010] More preferably, by weight, the hybrid fiber is mainly composed of 2 to 4 parts modified basalt fiber, 1 to 2 parts PVA fiber and 1 to 2 parts ultra-high molecular weight polyethylene (PE) fiber.

[0011] More preferably, by weight, the hybrid fiber is mainly composed of 3 parts modified basalt fiber, 2 parts PE fiber and 1 part PVA fiber.

[0012] Preferably, the basalt fibers are a combination of basalt fibers of different lengths.

[0013] More preferably, the basalt fiber is a combination of at least two of the basalt fibers with lengths of 6 mm, 9 mm, 12 mm, and 18 mm.

[0014] More preferably, the basalt fibers are a combination of basalt fibers with lengths of 6 mm and 18 mm in a mass ratio of 1:1.

[0015] More preferably, the basalt fibers are a combination of basalt fibers with lengths of 6 mm, 9 mm and 18 mm in a mass ratio of 1:1:1.

[0016] Preferably, the basalt fiber has a diameter of 15-19 μm, an elongation at break of 2.5%-3.1%, an elastic modulus of 98-110 MPa, and a tensile strength greater than 1.25 GPa.

[0017] More preferably, the diameter of the basalt fiber is 17 μm.

[0018] Preferably, the basalt fiber modification method is as follows: basalt fiber is reacted with a coupling agent under high temperature conditions to obtain modified basalt fiber.

[0019] Preferably, the high temperature is 90℃~100℃; more preferably, the high temperature is 95℃.

[0020] Preferably, the reaction time is 6 to 7 hours; more preferably, the reaction time is 6.5 hours.

[0021] Preferably, the weight of the coupling agent / the weight of the basalt fiber is (0.7-0.8):1.

[0022] Preferably, the coupling agent is at least one of KH-550, KH560, and KH570.

[0023] Preferably, the ultra-high performance fiber-reinforced concrete further includes 2 to 5 parts of steel fibers.

[0024] Preferably, the steel fiber is recycled steel fiber from waste tires.

[0025] Preferably, the cement is at least one of silicate cement and slag cement.

[0026] Preferably, the density of the silica fume is 1.8–2.5 g / cm³. 3 The silica content in silica ash is 85% to 95%.

[0027] More preferably, the density of the silica fume is 2.232 g / cm³. 3 The silica content in the silica ash is 93.7%.

[0028] Preferably, the fly ash is Grade I fly ash with a density of 2.0–2.6 g / cm³. 3 .

[0029] More preferably, the fly ash has a density of 2.4 g / cm³. 3 .

[0030] Preferably, the quartz sand has a fineness of 20-40 mesh and a density of 2.2-2.8 g / cm³. 3 .

[0031] More preferably, the density of the quartz sand is 2.654 g / cm³. 3 .

[0032] Preferably, the density of the quartz powder is 2.4–2.8 g / cm³. 3 .

[0033] A second aspect of the present invention provides a method for preparing the ultra-high performance fiber-reinforced concrete described in the first aspect, comprising the following steps:

[0034] (1) Modified basalt fiber, PVA fiber and PE fiber are mixed to obtain hybrid fiber;

[0035] (2) Mix cement, fly ash, silica fume and water-reducing agent; then add water, quartz powder and quartz sand in sequence;

[0036] (3) Add mixed fibers, use ultrasonic dispersion to mix and disperse, and then stir to obtain concrete slurry;

[0037] (4) After the concrete slurry is hardened, ultra-high performance fiber-reinforced concrete is obtained.

[0038] Preferably, the mixing of cement, fly ash, silica fume and water-reducing agent in step (2) is completed in a concrete mortar mixer; the mixing time is 6 to 10 minutes; the mixing speed is 100 to 150 rpm; more preferably, the mixing time is 8 minutes.

[0039] Preferably, in step (2), water, quartz powder and quartz sand are added and stirred separately; first, the stirring speed is increased to 500-800 rpm for 4-6 minutes, and then the stirring speed is increased to 500-800 rpm for 8-12 minutes.

[0040] More preferably, in step (2), water, quartz powder and quartz sand are added and stirred separately; first, stir at a speed of 200-300 rpm for 5 minutes, then increase the stirring speed to 500-800 rpm and continue stirring for 10 minutes.

[0041] Preferably, the ultrasonic frequency in step (2) is 15-20 kHz and the ultrasonic dispersion time is 2-4 min; more preferably, the ultrasonic dispersion time is 3 min.

[0042] Preferably, the stirring speed in step (2) is 500-800 rpm and the stirring time is 5-15 min; more preferably, the stirring time is 5 min.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) In the ultra-high performance fiber-reinforced concrete provided by this invention, the disordered distribution of modified basalt fibers, PVA fibers, and PE fibers inside the concrete forms a three-dimensional network structure, constituting a more uniform support system, which has a certain inhibitory effect on the generation and propagation of cracks. The synergistic effect of the mixture of different fibers achieves the effect of strengthening and toughening the ultra-high performance fiber-reinforced concrete, resulting in a concrete structure with better flexural strength and compressive strength.

[0045] (2) The mixing ratios of different modified basalt fibers, PVA fibers, and PE fibers, as well as the mixing of basalt fibers of different lengths, have a certain impact on the mechanical properties of ultra-high performance fiber-reinforced concrete. This invention provides a better mixing ratio of fiber types and fiber lengths, and the resulting ultra-high performance fiber-reinforced concrete has excellent mechanical properties, making it suitable for the performance requirements of concrete in harsh environments.

[0046] (3) In this invention, the modification treatment of basalt fiber significantly improves the uniformity of the mixing of concrete components and the resistance to water dispersion.

[0047] (4) In the technical solution described in this invention, the proportion of each raw material is obtained through multiple experiments. The prepared ultra-high performance fiber reinforced concrete has excellent mechanical properties and can be used for a long time in high-speed rail cable troughs and covers, pedestrian overpasses, lightweight bridge decks, low rib plate composite beams, steel frame arch bridges, building exteriors and repair and reinforcement structures. Attached Figure Description

[0048] Figure 1 The image shows a scanning electron microscope (SEM) image of the bending fracture morphology of the ultra-high performance fiber-reinforced concrete raw material prepared in Example 3.14, which is jointly reinforced by modified basalt fibers, PVA fibers, and PE fibers.

[0049] Figure 2 A scanning electron microscope image of the bending fracture morphology of plain concrete (i.e., without fiber reinforcement). Detailed Implementation

[0050] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments.

[0051] It should be understood that the terms "comprising," "including," "having," and similar terms used in the following embodiments are not intended to exclude the presence of any optional components, steps, or procedures, regardless of whether any optional components, steps, or procedures are specifically disclosed. For the avoidance of any doubt, unless stated to the contrary, all methods claimed by using the term "comprising" may include one or more additional steps, equipment parts or components, and / or substances. In contrast, the term "consisting of" excludes any components, steps, or procedures not specifically described or enumerated. Unless otherwise stated, the term "or" refers to members listed individually and in any combination.

[0052] In the following examples, unless otherwise specified, all parts are parts by mass, temperatures are expressed in °C or at ambient temperature, and pressures are at or near atmospheric pressure. Room temperature means 20–30 °C. Various variations and combinations of reaction conditions exist (e.g., component concentrations, desired solvents, solvent mixtures, temperature, pressure, and other reaction ranges) and conditions that can be used to optimize the purity and yield of the product obtained by the method. Only reasonable routine experiments are required to optimize such method conditions.

[0053] Example 1: A type of ultra-high performance fiber-reinforced concrete

[0054] An ultra-high performance fiber-reinforced concrete is made from the following raw materials: 45 parts cement, 36 parts silica fume, 50 parts fly ash, 25 parts quartz powder, 55 parts quartz sand, 4-8 parts mixed fibers, 2 parts water-reducing agent, and 100 parts water.

[0055] (1) Mixed fibers

[0056] The hybrid fiber comprises 2-4 parts modified basalt fiber, 1-2 parts PVA fiber, and 1-2 parts PE fiber. The modified basalt fiber is made from basalt fiber after modification treatment. The basalt fiber consists of basalt fibers of four different lengths: 6mm, 9mm, 12mm, and 18mm. The physical and mechanical properties of the basalt fiber, PVA fiber, and PE fiber are shown in Table 1. The basalt fiber used is dispersed chopped basalt fiber produced by Zhengzhou Dengdian Basalt Fiber Co., Ltd., with lengths of 6mm, 9mm, 12mm, and 18mm. The PVA fiber used is purchased from Kuraray Co., Ltd. of Japan, with a fiber length of 12mm. The PE fiber used is purchased from Hunan Zhongtai Special Equipment Co., Ltd., with a length of 12mm.

[0057] Table 1 Physical and mechanical properties of basalt fiber, PVA fiber, and PE fiber

[0058]

[0059] (2) Cement

[0060] The chemical composition of cement in the raw materials for preparing ultra-high performance fiber-reinforced concrete is shown in Table 2.

[0061] Table 2 Main Chemical Components of Cement

[0062]

[0063] (3) Silica ash

[0064] Silica fume, also known as microsilica powder, is a dust produced during metal smelting. It is a highly reactive pozzolanic material. Adding an appropriate amount of silica fume to concrete can significantly improve its compressive strength, flexural strength, impermeability, and abrasion resistance.

[0065] The silica fume used in this invention has a density of 2.232 g / cm³. 3 The composition and content of the components are shown in Table 3.

[0066] Table 3. Composition and content of silica fume

[0067]

[0068] (4) Fly ash

[0069] Fly ash is a byproduct of coal combustion, primarily originating from power plants and other sources. As a mineral admixture, fly ash possesses many beneficial properties: it contains abundant silicate substances that can react with calcium compounds to form gel-like substances that fill voids in concrete, reducing its autogenous shrinkage and improving its density and durability.

[0070] The fly ash used in this invention is Grade I fly ash with a density of 2.4 g / cm³. 3 The composition and content of the components are shown in Table 4.

[0071] Table 4 Composition and content of fly ash

[0072]

[0073] (5) Quartz Sand

[0074] Quartz sand is mainly used as a filler and aggregate in ultra-high performance fiber-reinforced concrete. Adding an appropriate amount of quartz sand to ultra-high performance fiber-reinforced concrete can improve the compactness, durability, and thermal stability of the concrete because quartz sand particles are uniform in size and have good rigidity and thermal stability.

[0075] This invention uses 20-40 mesh quartz sand with a density of 2.654 g / cm³. 3 The composition and content of the components are shown in Table 5.

[0076] Table 5 Composition content of quartz sand

[0077]

[0078] (6) Quartz powder

[0079] Quartz powder primarily functions as a filler in the preparation of ultra-high performance fiber-reinforced concrete (UHVFT). It fills the microscopic pores and cracks in UHVFT, effectively reducing its porosity and increasing its bulk density. Simultaneously, quartz powder's high hardness forms a high-strength cementitious substance, enhancing the compressive, flexural, and tensile strength of UHVFT.

[0080] This invention uses 325-mesh quartz powder with a density of 2.626 g / cm³. 3 .

[0081] (7) Water-reducing agent

[0082] The water-reducing agent used in the raw materials for preparing the ultra-high performance fiber-reinforced concrete is model ZY-HPWR-S. Detailed parameters of the water-reducing agent are shown in Table 6.

[0083] Table 6 Detailed parameters of water-reducing agents

[0084]

[0085] Example 2: A method for preparing ultra-high performance fiber-reinforced concrete

[0086] The preparation method of the ultra-high performance fiber-reinforced concrete includes the following steps:

[0087] (1) Basalt fiber modification: Basalt fiber was reacted with coupling agent KH-550 at 95℃ for 6.5h to obtain modified basalt fiber; wherein, the weight of KH-550 / weight of basalt fiber = (0.7-0.8):1;

[0088] (2) Prepare hybrid fibers by mixing modified basalt fibers, PVA fibers and PE fibers; weigh cement, silica fume, fly ash, quartz powder, quartz sand, hybrid fibers, water-reducing agent and water according to the mass proportions described in Example 1;

[0089] (3) Pour cement, fly ash, silica fume and water-reducing agent into the concrete mortar mixer, turn on the concrete mortar mixer and dry mix for 8 minutes at a speed of 100-150 rpm;

[0090] (4) Add water, quartz powder, and quartz sand in sequence and stir for 5 minutes each. The stirring speed is 200-300 rpm. Then, switch from slow stirring to fast stirring for 10 minutes. The fast stirring speed is 500-800 rpm.

[0091] (5) Add mixed fibers and use ultrasonic dispersion to mix and disperse them. The ultrasonic frequency is 15-20KHz and the ultrasonic dispersion time is 3 minutes. Then stir quickly at a speed of 500-800 rpm for 10 minutes to obtain concrete slurry.

[0092] (6) The ultra-high performance fiber-reinforced concrete is obtained by pouring and curing the concrete slurry.

[0093] Example 3: Effect of different fiber dosages on the mechanical properties of ultra-high performance fiber-reinforced concrete

[0094] To investigate the effects of the mixing ratio of modified basalt fiber, PVA fiber, and PE fiber, as well as the length of basalt fiber, on the mechanical properties of ultra-high performance fiber-reinforced concrete, Examples 3.1 to 3.17 were set up. The difference between the examples lies in the fiber content. The fiber content of each example is shown in Table 7.

[0095] To test the mechanical properties of the ultra-high performance fiber-reinforced concrete provided in Examples 3.1 to 3.17, corresponding concrete specimens were prepared. The preparation process is as follows: At room temperature, a layer of oil was brushed onto the inner surface of a 40mm×40mm×160mm triple mold to facilitate subsequent demolding; half of the concrete slurry was poured into the mold, and air was removed using a tool. The mold was then placed on a cement mortar vibrating table and vibrated 60 times; the other half of the concrete slurry was poured into the mold, air was removed again, and the mold was placed on the vibrating table and vibrated 60 times; finally, the specimen was smoothed. After smoothing, a layer of plastic wrap was placed on the surface of the specimen. After 24 hours, the mold was removed, and the specimen was placed in a curing room for curing. The curing conditions were a temperature of 20 degrees Celsius, a humidity of 95%, and a standard curing period of 28 days.

[0096] Mechanical performance testing was conducted in accordance with the requirements of the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T50081-2019). After the test blocks were cured for 28 days, they were promptly removed from the curing environment for compressive strength and flexural strength tests. The test data are shown in Table 7.

[0097] Table 7 Compressive and flexural strength test data

[0098]

[0099]

[0100] As shown in Table 7:

[0101] (1) In Example 3.5, PE fiber, PVA fiber and 12mm modified basalt fiber were mixed to make ultra-high performance fiber reinforced concrete with high compressive and flexural strength. That is, when the mass parts of modified basalt fiber, PE fiber and PVA fiber are 3 parts, 2 parts and 1 part respectively, the ultra-high performance fiber reinforced concrete has better mechanical properties.

[0102] (2) The use of modified basalt fibers of different lengths is to fully utilize their advantages. The combined effect of different fiber lengths can more effectively inhibit crack propagation, thereby improving the mechanical properties and ductility of concrete. When two modified basalt fibers of different lengths are mixed, the mixture of 6mm and 18mm modified basalt fibers has a greater improvement on the mechanical properties of concrete; when three modified basalt fibers of different lengths are mixed, the mixture of 6mm, 9mm and 18mm modified basalt fibers has a greater improvement on the mechanical properties of concrete.

[0103] (3) It is not that the four different lengths of modified basalt fibers are mixed at the same time. The better the mechanical properties of the concrete, the better the compressive strength and flexural strength of Example 3.17 are. They are not as good as the mechanical properties of two and three different lengths of modified basalt fibers.

[0104] It should be noted that the inventors also conducted research on the mixing of unmodified basalt fibers of different lengths with PE and PVA fibers. When the basalt fibers were not modified, the mechanical properties of the prepared concrete were not as good as those of the concrete prepared with modified basalt fibers. The modification treatment with basalt fibers further improved the uniformity of the mixing of the various components of the concrete and its resistance to water dispersion.

[0105] Furthermore, the inventors performed scanning electron microscopy to characterize the flexural fracture morphology of the ultra-high performance fiber-reinforced concrete obtained in Example 3.14 and a plain concrete (i.e., without fiber reinforcement), and the results are as follows. Figure 1 , Figure 2 As shown. The raw materials for preparing the plain concrete are the same as those in Example 1, except that they are free of mixed fibers, and the preparation method is the same as in Example 2.

[0106] Depend on Figure 1 , Figure 2 It is known that the combination of modified basalt fibers, PE fibers, and PVA fibers can bridge cracks and inhibit the propagation and generation of cracks in ultra-high performance fiber-reinforced concrete matrices. Furthermore, the fibers dissipate a significant amount of energy during the pull-out and breakage process, thereby further enhancing the strength and toughness of the ultra-high performance fiber-reinforced concrete matrix. Simultaneously, the blending of different fibers produces a synergistic effect, allowing each fiber to fully exert its respective role at different structural levels and loading stages, complementing each other to achieve a toughening and strengthening effect.

[0107] As shown in Table 7, the ultra-high performance fiber-reinforced concrete prepared in Example 3.14 has the best mechanical properties. Multiple sets of mechanical property tests were carried out on the ultra-high performance fiber-reinforced concrete prepared in this example, and the test results are shown in Table 8.

[0108] Table 8. Results of compressive and flexural strength tests on ultra-high performance fiber-reinforced concrete prepared in Example 3.14

[0109] Collapse Expansion ≥750mm 28-day compressive strength ≥188MPa 28d flexural strength ≥39MPa 28-day tensile strength ≥12MPa 28-day shrinkage rate <![CDATA[Less than 150×10 -6 >

[0110] Table 8 shows that the test results further demonstrate that the ultra-high performance fiber-reinforced concrete provided by this invention can be used in extreme environments for a long time, such as high-speed rail cable troughs and covers, pedestrian bridges, lightweight bridge decks, low-ribbed composite beams, steel arch bridges, building exterior finishes, and repair and reinforcement structures.

[0111] It should be understood that the above-described embodiments are only some preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A type of ultra-high performance fiber-reinforced concrete, characterized in that, It is mainly made of the following raw materials in parts by weight: 60-65 parts cement, 15-36 parts silica fume, 20-50 parts fly ash, 20-25 parts quartz powder, 45-55 parts quartz sand, 4-8 parts mixed fiber, 1-2 parts water-reducing agent, and 20-100 parts water. The mixed fiber, by weight, is mainly composed of 2-4 parts modified basalt fiber, 1-2 parts PVA fiber, and 1-2 parts PE fiber. The modified basalt fiber is made from basalt fiber after modification treatment. The basalt fiber is a combination of basalt fibers with lengths of 6mm, 9mm, and 18mm in a weight ratio of 1:1:

1. The modification method is as follows: basalt fiber and coupling agent are placed under high temperature conditions for chemical modification to obtain modified basalt fiber; the high temperature is 90℃~100℃.

2. The concrete according to claim 1, characterized in that, The coupling agent is at least one of KH-550, KH560, and KH570; the weight ratio of the coupling agent to the basalt fiber is (0.7-0.8):

1.

3. The concrete according to claim 1, characterized in that, The cement is at least one of silicate cement and slag cement; the silica fume density is 1.8–2.5 g / cm³. 3 The silica content in the silica ash is 85% to 95%.

4. The concrete according to claim 1, characterized in that, The density of the fly ash is 2.0–2.6 g / cm³. 3 The quartz sand has a fineness of 20–40 mesh and a density of 2.2–2.8 g / cm³. 3 .

5. The concrete according to claim 1, characterized in that, The basalt fibers have a diameter of 15–19 μm, an elongation at break of 2.5%–3.1%, an elastic modulus of 98–110 MPa, and a tensile strength greater than 1.25 GPa.

6. The method for preparing ultra-high performance fiber-reinforced concrete according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Modified basalt fiber, PVA fiber and PE fiber are mixed to obtain hybrid fiber; (2) Mix cement, fly ash, silica fume and water-reducing agent; then add water, quartz powder and quartz sand in sequence; (3) Add mixed fibers, use ultrasonic dispersion to mix and disperse, and then stir to obtain concrete slurry; (4) Ultra-high performance fiber-reinforced concrete is obtained after the concrete slurry hardens; the ultrasonic frequency is 15-20 KHz and the ultrasonic dispersion time is 2-4 min.

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