Functional composite capsule servo fiber for concrete and preparation method

Abstract

The invention relates to a functional composite capsule servo fiber for concrete and a preparation method thereof. The method comprises the following steps: 1, pretreating a base bamboo fiber; 2, preparation of built-in skeleton composite fibers: uniformly winding polyformaldehyde fibers on the surfaces of the pretreated matrix bamboo fibers by adopting winding equipment to form a skeleton composite fiber structure; 3, preparing a composite capsule body fiber structure: preparing the pretreated base body bamboo fibers into an outer wrapping bamboo fiber capsule through a balling winding process, and reserving micropores in the top of the outer wrapping bamboo fiber capsule; the built-in framework composite fibers are packaged in the externally-wrapped bamboo fiber capsule to form a composite capsule body fiber structure; 4, preparing a functional reinforced repair material; and 5, preparation of the functional composite capsule servo fiber for the concrete: uniformly filling the functional reinforced repair material into the composite capsule fiber structure through the micropores, and finally sealing the micropores to form the functional composite capsule servo fiber for the concrete.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and particularly relates to a functional composite capsule servo fiber for concrete and a preparation method thereof. Background Art

[0002] High Performance Concrete (HPC) has been widely used in major engineering fields (such as long-span bridges, super high-rise buildings, ocean engineering, etc.) due to its excellent mechanical properties (such as high strength and high modulus) and outstanding durability (such as impermeability and freeze-thaw resistance). However, HPC still faces severe technical challenges in practical applications: due to its characteristics of low water-binder ratio and high cementitious material dosage, significant thermal stress will be generated during the hydration process. Coupled with the combined action of autogenous shrinkage and drying shrinkage, microcracks are extremely likely to occur during the early stage and long-term use. These microcracks will not only reduce the mechanical properties of concrete, but also become the penetration channels for harmful media (such as chloride ions and carbon dioxide), seriously damaging the durability and service life of the structure.

[0003] Therefore, how to provide a functional composite capsule servo fiber for concrete and a preparation method thereof to effectively solve the cracking problem of HPC is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0004] Aiming at the cracking problem of traditional high-performance concrete, the present invention proposes a functional composite capsule servo fiber for concrete and a preparation method thereof, which organically combines fiber reinforcement and self-healing mechanisms, realizes an innovative capsule design with "a composite capsule fiber structure based on an internal skeleton composite fiber and an outer bamboo fiber capsule, and a functional reinforced repair material filler" as the core, and has a dual quality guarantee mechanism of "active defense + passive repair" and a multi-quality guarantee system of "structural composite + functional composite". It can not only effectively enhance the workability, mechanical properties, crack resistance and durability of concrete, realize the self-healing function of concrete cracks, but also effectively reduce the production cost of concrete and reduce the self-weight of concrete, which has important theoretical scientific value and engineering practical significance.

[0005] To solve the above technical problems, the present invention includes the following technical solutions: A preparation method of a functional composite capsule servo fiber for concrete, comprising the following steps: Step S1, pretreatment of matrix bamboo fiber: Select bamboo fiber for degreasing, alkali treatment and drying, and perform surface treatment on the bamboo fiber with a silane coupling agent; Step S2, preparation of internal skeleton composite fiber: Use a winding device to evenly wind polyoxymethylene fiber on the surface of the pretreated matrix bamboo fiber to form a skeleton composite fiber structure; Step S3. Preparation of composite capsule fiber structure: The pretreated matrix bamboo fiber is made into an outer bamboo fiber capsule through a ball winding process, and micropores with a pore diameter of 50 - 100 μm are reserved at the top of the outer bamboo fiber capsule; and the internal framework composite fiber is encapsulated in the outer bamboo fiber capsule through microfluidics technology or electrospinning method to form a composite capsule fiber structure; Step S4. Preparation of functional enhanced repair material: The first step. Pretreatment of raw materials: First, perform the modification treatment of calcium carbonate whiskers: Select a silane coupling agent with a mass fraction of 1 - 3% as the modifier, stir at a speed of 300 - 500 rpm for 30 - 60 min under the condition of 60 - 80 °C, and perform surface modification on calcium carbonate whiskers with a purity of ≥99%; Then, perform the dispersion treatment of nano - silica: Select a polycarboxylate - based dispersant as the ultrasonic dispersant, and perform ultrasonic treatment on nano - SiO2 in an aqueous solution; The second step. Mixing and soaking: Mix the modified calcium carbonate whiskers and nano - SiO2 according to a mass ratio of 7:3, add deionized water according to a solid - liquid ratio of 1:5, and stir at 50 - 60 °C for 1 - 1.5 h to form a mixed slurry; The third step. Drying and dehydration: Transfer the mixed slurry to a vacuum drying oven and dry it until the moisture content ≤5%, so that the dried composite material has a porous network structure; The fourth step. Cutting and forming: Use a micron - level cutting machine, adjust the blade spacing to 50 - 100 μm, and cut the dried composite material into short fibers with a length of 1.0 - 5.0 mm to obtain a functional enhanced repair material with a high specific surface area and microporous structure; Step S5. Preparation of functional composite capsule servo fiber for concrete: Through the micropores of the composite capsule fiber structure, uniformly fill the functional enhanced repair material into the composite capsule fiber structure, and finally seal the micropores to form a functional composite capsule servo fiber for concrete.

[0006] Furthermore, the step S1 includes: Select bamboo fibers with a diameter of 50 - 200 μm and a length of 10 - 15 mm, degrease them, soak them in 5% NaOH solution for 24 h, then dry them to a constant weight at 60 °C, treat them with KH - 550 with a mass fraction of 2% at 60 °C for 1 h, and then rinse them with deionized water until neutral.

[0007] Furthermore, adjust the winding equipment speed to 200 - 300 rpm, select a winding angle of 45 ± 5°, a winding tension of 0.5 - 1.0 N, control the ambient temperature at 23 ± 2 °C, and perform heat treatment at 120 °C for 10 min after winding to form a stable physical bond between POM fiber and bamboo fiber.

[0008] Further, the diameter of the calcium carbonate whiskers is 0.5 - 2 μm, and the aspect ratio is 20 - 50.

[0009] Further, the particle size of the nano - SiO₂ is 10 - 30 nm, and the specific surface area ≥ 200 m² / g.

[0010] The present invention also provides a functional composite capsule servo fiber for concrete, including a composite capsule fiber structure formed by an internal - skeleton composite fiber layer, an outer - wrapped bamboo fiber capsule, and a functional enhanced repair material filled between the two.

[0011] Compared with the prior art, the beneficial effects of the present invention are mainly as follows: (1) The functional composite capsule servo fiber for concrete provided by the present invention adopts a composite capsule fiber structure based on an internal - skeleton composite fiber and an outer - wrapped bamboo fiber capsule, which can not only significantly improve the workability, mechanical properties, crack - resistance and long - term durability of the concrete matrix, effectively reduce the density and production cost of the concrete, but also make the most of renewable natural bamboo resources and avoid carbon dioxide emissions during the production of steel fibers. Therefore, it has good social and economic benefits. Moreover, this fiber technology can endow the concrete with a dual quality assurance mechanism of "active defense + passive repair" and a multi - element quality assurance system of "structural composite + functional composite".

[0012] (2) The functional composite capsule servo fiber for concrete and its preparation method provided by the present invention adopt a functional enhanced repair material with "calcium carbonate whiskers + nano - silica" as the core to fill the composite capsule fiber structure. In the case of adverse cracking of the concrete, the calcium carbonate whiskers, as a micron - level reinforcement phase, can provide instant mechanical support for the concrete through the whisker pull - out effect and crack deflection mechanism. At the same time, the nano - silica will react with the cement hydration products for a second time to generate new C - S - H gels, filling the micro - cracks of the concrete and completing the self - repair of the structure, thereby improving the mechanical strength and long - term durability of the concrete structure and ensuring the quality and long - term service safety of the concrete structure. Specific Embodiments

[0013] The following further details a functional composite capsule servo fiber for concrete and its preparation method provided by the present invention with reference to specific embodiments. According to the following description, the advantages and features of the present invention will be clearer.

[0014] The following describes the functional composite capsule servo fiber for concrete and its preparation method of the present invention.

[0015] Specifically, the preparation method of a functional composite capsule servo fiber for concrete is as follows: Step S1 Matrix bamboo fiber pretreatment: Select high-quality bamboo fibers with a diameter of 50 - 200 μm and a length of 10 - 15 mm. Through pre-treatment processes such as degreasing, alkali treatment by soaking in 5% NaOH solution for 24 h, and drying by baking at 60 °C to constant weight, the interfacial bonding performance with the polymer is improved. Then, the bamboo fibers are surface-treated with a silane coupling agent (KH-550) under the conditions: the mass fraction of KH-550 is 2%, the temperature is 60 °C, and the time is 1 h. After treatment, it is rinsed with deionized water until neutral.

[0016] Step S2 Preparation of the internal skeleton composite fiber: Using a precision winding device, adjust the rotation speed to 200 - 300 rpm, and evenly wind polyoxymethylene (POM) fibers with a diameter of 20 - 50 μm on the surface of the pre-treated matrix bamboo fibers to form a "bamboo fiber - POM fiber" skeleton composite fiber structure. The specific process control parameters are: winding angle 45 ± 5° to optimize stress transfer, winding tension 0.5 - 1.0 N to ensure winding tightness, and the ambient temperature is selected as 23 ± 2 °C to control the crystallinity of the POM fibers. After winding, it is heat-treated at 120 °C for 10 min to form a stable physical bond between the POM fibers and the bamboo fibers, thus forming the internal skeleton composite fiber.

[0017] Step S3 Preparation of the composite capsule fiber structure: The pre-treated matrix bamboo fibers are made into an outer bamboo fiber capsule through a ball-forming winding process, and a controllable release micropore with a pore diameter of 50 - 100 μm is reserved at the top of the outer bamboo fiber capsule. Further, the internal skeleton composite fiber is encapsulated in the outer bamboo fiber capsule by microfluidics technology or electrospinning method to form a composite capsule fiber structure.

[0018] Step S4 Preparation of the functional enhanced repair material: The functional enhanced repair material is a composite repair material system based on calcium carbonate whiskers (CaCO3 whiskers) and nano-silica (nano-SiO2), with the characteristics of high activity, controllable release, and self-healing enhancement. Its manufacturing process includes the following key steps: The first step Raw material pre-treatment: First, the modification treatment of calcium carbonate whiskers: Select calcium carbonate whiskers with high purity (≥99%), with a diameter of 0.5 - 2 μm and an aspect ratio of 20 - 50. Use a silane coupling agent (KH-550) with a mass fraction of 1 - 3% as the modifier, and stir at a rotation speed of 300 - 500 rpm at 60 - 80 °C for 30 - 60 min to perform surface modification on the calcium carbonate whiskers and improve its compatibility with the cement matrix.

[0019] Then, nano-silica dispersion treatment: Select nano-SiO2 (particle size 10 - 30 nm, specific surface area ≥ 200 m² / g), and use a polycarboxylate-based dispersant (PCE, dosage 0.5 - 1%) as the ultrasonic dispersant to perform ultrasonic treatment on nano-SiO2 in an aqueous solution. The treatment conditions are 40 kHz and 30 min to prevent nanoparticle agglomeration.

[0020] The second step is mixing and soaking: Mix the modified calcium carbonate whiskers and nano-SiO2 at a mass ratio of 7:3, add deionized water with a solid-liquid ratio of 1:5, and stir at 50 - 60 °C for 1 - 1.5 h to fully infiltrate the materials.

[0021] The third step is drying and dehydration: Transfer the mixed slurry to a vacuum drying oven, control the temperature at 100 - 150 °C, and the vacuum degree at -0.08 MP to dry until the moisture content ≤ 5%. After drying, the composite material has a porous network structure, facilitating subsequent wire-cutting processing.

[0022] The fourth step is wire-cutting and forming: Use a micro-level wire-cutting machine, adjust the blade spacing to 50 - 100 μm, cut the dried composite material into short fibers with a length of 1.0 - 5.0 mm, and obtain a functional enhanced repair material with a high specific surface area and microporous structure, which can efficiently adsorb Ca²⁺ in the cement paste and promote the secondary hydration reaction at the crack.

[0023] Step S5: Preparation of functional composite capsule servo fibers for concrete: Uniformly fill the functional enhanced repair material into the composite capsule fiber structure through a controllable release micropore, and then seal the controllable release micropore to form functional composite capsule servo fibers for concrete.

[0024] The functional composite capsule servo fibers for concrete of the present invention include a composite capsule fiber structure formed by an inner built-in skeleton composite fiber layer, an outer bamboo fiber capsule, and a functional enhanced repair material filled between the two. The functional composite capsule servo fibers for concrete can endow the concrete with a dual quality guarantee mechanism of "active defense + passive repair" and a multi-quality guarantee system of "structural composite + functional composite".

[0025] The following details the characteristics of the ultra-high performance concrete prepared by the preparation method of the present invention in combination with specific embodiments.

[0026] Example 1

[0027] To verify the actual effect of the functional composite capsule servo fibers for concrete proposed by the present invention, a comparative test plan was designed, which was divided into 6 groups of specimens, specifically as follows: (1) Control group: UHPC (Ultra-High Performance Concrete) without servo fibers, C80 high-strength high-performance concrete, and C60 high-strength high-performance concrete.

[0028] (2) Invention group: Under the same mix ratio, UHPC (Ultra-High Performance Concrete), C80 high-strength high-performance concrete, and C60 high-strength high-performance concrete with the functional composite capsule servo fibers for concrete of the present invention added, and the volume fraction incorporated is 1.5%. The mix ratio design of each group is shown in Table 1.

[0029] Table 1: Mix ratio design table for test groups

[0030] 2. Test methods and result analysis (1) Slump flow test Referring to GB / T 50080-2016 "Standard Test Method for Properties of Fresh Concrete", the fluidity of fresh concrete was tested. The slump flow test results of the concrete in each group are shown in Table 2.

[0031] Table 2: Slump flow test results of concrete

[0032] It can be seen that the slump flow of the concrete in the invention group increased by 8 - 12% compared with the control group, and the fibers were evenly dispersed without agglomeration.

[0033] (2) Compressive strength test Referring to GB / T 50081-2019 "Standard Test Method for Physical and Mechanical Properties of Concrete", the compressive strength at 28 days and 180 days was tested. The compressive strength test results of the concrete in each group are shown in Table 3.

[0034] Table 3: Compressive strength test results of concrete

[0035] It can be seen that the 28-day compressive strength of the invention group increased by 8 - 12% respectively compared with the control group; at the same time, the 180-day compressive strength of the invention group increased by 15 - 18% compared with the control group.

[0036] (3) Tensile strength test The splitting tensile test (GB / T 50081-2019) was adopted to test the tensile strength at 28 days and 180 days. The tensile strength test results of the concrete in each group are shown in Table 4.

[0037] Table 4: Tensile strength test results of concrete

[0038] It can be seen that the tensile strength of the invention group 28d is 15 - 20% higher than that of the control group, and the tensile strength of the invention group 180d is 17 - 20% higher than that of the control group.

[0039] (4)Autogenous shrinkage test Referring to ASTM C1581, the autogenous shrinkage rate of concrete in the early stage (1 - 7d) was tested. The autogenous shrinkage test results of each group of concrete are shown in Table 5.

[0040] Table 5: Autogenous shrinkage test results of concrete

[0041] It can be seen that the autogenous shrinkage rate of the invention group is 25 - 30% lower than that of the control group.

[0042] (5)Observation of crack development The change in crack width within 180d was monitored by digital image correlation technology (DIC). The crack development results of each group of concrete are shown in Table 6.

[0043] Table 6: Crack development results of concrete mm

[0044] It can be seen that the maximum crack width of the control group reaches 0.219 - 0.300mm, while the maximum crack width of the invention group is only 0.022 - 0.050mm, indicating that the repair efficiency of the invention group is over 85%.

[0045] In summary, using the functional composite capsule servo fiber for concrete of the present invention to prepare the concrete mixture can significantly improve the workability, mechanical properties and crack resistance of the concrete, with remarkable technical effects and high popularization and application value.

[0046] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above examples. The above - described examples only represent several embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A preparation method of a functional composite capsule servo fiber for concrete, characterized in that, It includes the following steps: Step S1, pretreatment of matrix bamboo fiber: Select bamboo fiber, degrease it, treat it with alkali and dry it, and use a silane coupling agent to perform surface treatment on the bamboo fiber; Step S2, preparation of internal skeleton composite fiber: Use a winding device to evenly wind polyoxymethylene fiber on the surface of the pretreated matrix bamboo fiber to form a skeleton composite fiber structure; Step S3, preparation of composite capsule fiber structure: Make the pretreated matrix bamboo fiber into an outer bamboo fiber capsule through a ball-forming winding process, and reserve micropores with a pore diameter of 50 - 100 μm at the top of the outer bamboo fiber capsule; And encapsulate the internal skeleton composite fiber in the outer bamboo fiber capsule through microfluidic technology or electrospinning method to form a composite capsule fiber structure; Step S4, preparation of functional enhanced repair material: The first step, pretreatment of raw materials: First, carry out the modification treatment of calcium carbonate whiskers: Select a silane coupling agent with a mass fraction of 1 - 3% as the modifier, stir at a speed of 300 - 500 rpm for 30 - 60 min under the condition of 60 - 80 °C, and perform surface modification on calcium carbonate whiskers with a purity ≥ 99%; Then, carry out the dispersion treatment of nano-silica: Select a polycarboxylate-based dispersant as the ultrasonic dispersant, and perform ultrasonic treatment on nano-SiO2 in an aqueous solution; The second step, mixing and soaking: Mix the modified calcium carbonate whiskers and nano-SiO2 according to a mass ratio of 7:3, add deionized water according to a solid-liquid ratio of 1:5, and stir at 50 - 60 °C for 1 - 1.5 h to form a mixed slurry; The third step, drying and dehydration: Transfer the mixed slurry to a vacuum drying oven and dry it until the moisture content ≤ 5%, so that the dried composite material has a porous network structure; The fourth step, cutting and forming: Use a micron-level cutting machine, adjust the blade spacing to 50 - 100 μm, and cut the dried composite material into short fibers with a length of 1.0 - 5.0 mm to obtain a functional enhanced repair material with a high specific surface area and a microporous structure; Step S5, preparation of functional composite capsule servo fiber for concrete: Through the micropores of the composite capsule fiber structure, evenly fill the functional enhanced repair material into the composite capsule fiber structure, and finally seal the micropores to form a functional composite capsule servo fiber for concrete.

2. The preparation method according to claim 1, wherein The said step S1 includes: Select bamboo fibers with a diameter of 50 - 200 μm and a length of 10 - 15 mm, degrease them, soak them in a 5% NaOH solution for 24 h, then bake them at 60 °C until constant weight, treat them with KH-550 with a mass fraction of 2% at 60 °C for 1 h, and rinse them with deionized water until neutral after treatment.

3. The preparation method according to claim 1, wherein, Adjust the winding device speed to 200 - 300 rpm, select a winding angle of 45 ± 5°, a winding tension of 0.5 - 1.0 N, control the ambient temperature at 23 ± 2 °C, and perform heat treatment at 120 °C for 10 min after winding to make the POM fiber and the bamboo fiber form a stable physical bond.

4. The preparation method according to claim 1, characterized in that, The diameter of the said calcium carbonate whiskers is 0.5 - 2 μm, and the aspect ratio is 20 - 50.

5. The preparation method according to claim 1, characterized in that, The particle size of the said nano-SiO2 is 10 - 30 nm, and the specific surface area ≥ 200 m² / g.

6. A functional composite capsule servo fiber for concrete, characterized in that, Using the preparation method described in any one of claims 1 to 5, the servo fiber comprises a composite capsule fiber structure formed by an inner built-in skeleton composite fiber layer, an outer bamboo fiber capsule, and a functional strengthening and repairing material filled between the two.

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