A functional composite capsule servo fiber for concrete and its preparation method

Abstract

The present invention relates to a functional composite capsule servo fiber for concrete and a preparation method thereof. The method includes: 1. Pretreatment of matrix bamboo fiber; 2. Preparation of built-in skeleton composite fiber: using a winding device to evenly wind polyoxymethylene fiber on the surface of the pretreated matrix bamboo fiber to form a skeleton composite fiber structure; 3. Preparation of composite capsule fiber structure: making the pretreated matrix bamboo fiber into an outer bamboo fiber capsule through a ball winding process, and reserving micropores at the top of the outer bamboo fiber capsule; encapsulating the built-in skeleton composite fiber in the outer bamboo fiber capsule to form a composite capsule fiber structure; 4. Preparation of functional enhanced repair material; 5. Preparation of functional composite capsule servo fiber for concrete: uniformly filling the functional enhanced repair material into the composite capsule fiber structure through the micropores, and finally sealing the micropores to form a functional composite capsule servo fiber for 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, high modulus) and outstanding durability (such as impermeability, 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, 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 needs to be urgently solved by those skilled in the art. 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-repair mechanisms, and realizes an innovative capsule design with the "composite capsule fiber structure based on an internal skeleton composite fiber and an outer bamboo fiber capsule, and a functional reinforced repair material filling body" as the core, with 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-repair function of concrete cracks, but also effectively reduce the production cost of concrete and reduce the self-weight of concrete, having important theoretical scientific value and engineering practical significance.

[0005] To solve the above technical problems, the present invention includes the following technical solutions:

[0006] A preparation method of a functional composite capsule servo fiber for concrete, comprising the following steps:

[0007] 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;

[0008] Step S2. Preparation of built-in 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;

[0009] 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 built-in skeleton composite fiber in the outer bamboo fiber capsule through microfluidic technology or electrospinning method to form a composite capsule fiber structure;

[0010] Step S4. Preparation of functional enhanced repair material:

[0011] The first step. Pretreatment of raw materials:

[0012] 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%;

[0013] 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;

[0014] 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;

[0015] 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;

[0016] 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;

[0017] 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.

[0018] Further, the step S1 includes: selecting bamboo fibers with a diameter of 50 - 200 μm and a length of 10 - 15 mm, degreasing them, soaking them in a 5% NaOH solution for 24 h, drying them at 60 °C to constant weight, treating them with 2% by mass of KH-550 at 60 °C for 1 h, and then rinsing them with deionized water until neutral.

[0019] Further, adjust the rotation speed of the winding equipment 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 the POM fibers and the bamboo fibers.

[0020] Further, the diameter of the calcium carbonate whiskers is 0.5 - 2 μm, and the aspect ratio is 20 - 50.

[0021] Further, the particle size of the nano-SiO2 is 10 - 30 nm, and the specific surface area is ≥ 200 m² / g.

[0022] The present invention also provides a functional composite capsule servo fiber for concrete, which includes a composite capsule fiber structure formed by an inner skeleton composite fiber layer, an outer bamboo fiber capsule, and a functional strengthening and repairing material filled between the two.

[0023] Compared with the prior art, the beneficial effects of the present invention are mainly as follows:

[0024] (1) The functional composite capsule servo fiber for concrete provided by the present invention adopts a composite capsule fiber structure based on an inner skeleton composite fiber and an outer 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 the 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 guarantee mechanism of "active defense + passive repair" and a multi-quality guarantee system of "structural composite + functional composite".

[0025] (2)The functional composite capsule servo fiber for concrete and its preparation method provided by the present invention adopt a functional reinforcement and repair material with "calcium carbonate whiskers + nano-silica" as the core to fill the composite capsule fiber structure. In the adverse situation of concrete cracking, calcium carbonate whiskers, as a micron-level reinforcement phase, can provide instant mechanical support for concrete through the whisker pull-out effect and crack deflection mechanism. At the same time, nano-silica will undergo a secondary reaction with cement hydration products to generate new C-S-H gels, filling the micro-cracks of concrete, completing self-repair of the structure, and then improving the mechanical strength and long-term durability of the concrete structure, ensuring the quality of the concrete structure and long-term service safety. Detailed Embodiments

[0026] The following further elaborates in detail on a functional composite capsule servo fiber for concrete and its preparation method provided by the present invention in combination with specific embodiments. According to the following description, the advantages and features of the present invention will be clearer.

[0027] The following describes the functional composite capsule servo fiber for concrete and its preparation method of the present invention.

[0028] Specifically, the preparation method of a functional composite capsule servo fiber for concrete is as follows:

[0029] Step S1 Pretreatment of the matrix bamboo fiber:

[0030] Select high-quality bamboo fibers with a diameter of 50 - 200μm and a length of 10 - 15mm, and perform pretreatment processes such as degreasing, alkali treatment by soaking in 5% NaOH solution for 24h, and drying at 60°C to constant weight to improve its interfacial bonding performance with the polymer. Then, the bamboo fibers are surface-treated with a silane coupling agent (KH-550), and the treatment conditions are: the mass fraction of KH-550 is 2%, the temperature is 60°C, and the time is 1h. After treatment, it is rinsed with deionized water until neutral.

[0031] Step S2 Preparation of the built-in skeleton composite fiber:

[0032] Using a precision winding device, adjust the rotation speed to 200 - 300rpm, and evenly wind polyoxymethylene (POM) fibers with a diameter of 20 - 50μm on the surface of the pretreated matrix bamboo fibers to form a "bamboo fiber - POM fiber" skeleton composite fiber structure. The specific process control parameters are: the winding angle is 45 ± 5° to optimize stress transfer, the winding tension is 0.5 - 1.0N to ensure the 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 10min to form a stable physical bond between the POM fibers and the bamboo fibers, forming the built-in skeleton composite fiber.

[0033] Step S3 Preparation of the composite capsule fiber structure:

[0034] The pretreated matrix bamboo fiber is made into an outer bamboo fiber capsule through a ball winding process, and a controllable release micropore is reserved at the top of the outer bamboo fiber capsule. The pore diameter of the micropore is 50 - 100 μm. Further, 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.

[0035] Step S4 Preparation of the functional enhanced repair material:

[0036] 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:

[0037] The first step is raw material pretreatment:

[0038] 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 speed of 300 - 500 rpm for 30 - 60 min at 60 - 80 °C to perform surface modification on the calcium carbonate whiskers and improve its compatibility with the cement matrix.

[0039] Then, the dispersion treatment of nano-silica: 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.

[0040] The second step is mixing and soaking:

[0041] Mix the modified calcium carbonate whiskers and nano-SiO2 in 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.

[0042] The third step is drying and dehydration:

[0043] 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, which is convenient for subsequent wire cutting processing.

[0044] The fourth step is wire cutting and forming:

[0045] Using a micron-level wire cutter, 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, thus obtaining a functional reinforcing and repairing material with a high specific surface area and a microporous structure, which can efficiently adsorb Ca²⁺ in the cement paste and promote the secondary hydration reaction at the crack.

[0046] Step S5: Preparation of the functional composite capsule servo fiber for concrete

[0047] Through the controllable release micropores, uniformly fill the functional reinforcing and repairing material into the composite capsule fiber structure, and then seal the controllable release micropores to form the functional composite capsule servo fiber for concrete.

[0048] The functional composite capsule servo fiber for concrete of the present invention includes a composite capsule fiber structure formed by an inner built-in skeleton composite fiber layer, an outer bamboo fiber capsule, and a functional reinforcing and repairing material filled between the two. This functional composite capsule servo fiber for concrete enables the concrete to have a dual quality assurance mechanism of "active defense + passive repair" and a multi-quality assurance system of "structural composite + functional composite".

[0049] The following details the characteristics of the ultra-high performance concrete prepared by the preparation method of the present invention with specific embodiments.

[0050] Example 1

[0051] To verify the actual effect of the functional composite capsule servo fiber for concrete proposed by the present invention, a comparative test scheme was designed, which was divided into 6 groups of specimens, specifically as follows:

[0052] (1) Control group: UHPC (ultra-high performance concrete) without servo fiber, C80 high-strength high-performance concrete, and C60 high-strength high-performance concrete.

[0053] (2) Invention group: UHPC (ultra-high performance concrete), C80 high-strength high-performance concrete, and C60 high-strength high-performance concrete with the addition of the functional composite capsule servo fiber for concrete of the present invention under the same mix ratio, and the incorporated volume fraction is 1.5%. The mix ratio design of each group is shown in Table 1.

[0054] Table 1: Mix ratio design table of test groups

[0055]

[0056] 2. Test methods and result analysis

[0057] (1) Slump flow test

[0058] Refer to GB / T 50080-2016 "Standard Test Method for Properties of Fresh Concrete", and test the flowability of fresh concrete. The test results of the slump flow of concrete for each group are shown in Table 2.

[0059] Table 2: Test Results of Slump Flow of Concrete

[0060]

[0061] It can be seen that the slump flow of the concrete in the invention group is 8-12% higher than that in the control group, and the fibers are evenly dispersed without agglomeration.

[0062] (2) Compressive Strength Test

[0063] Refer to GB / T 50081-2019 "Standard Test Method for Physical and Mechanical Properties of Concrete", and test the compressive strength at 28d and 180d. The test results of the compressive strength of concrete for each group are shown in Table 3.

[0064] Table 3: Test Results of Compressive Strength of Concrete

[0065]

[0066] It can be seen that the 28d compressive strength of the invention group is 8-12% higher than that of the control group respectively; at the same time, the 180d compressive strength of the invention group is 15-18% higher than that of the control group.

[0067] (3) Tensile Strength Test

[0068] Adopt the splitting tensile test (GB / T 50081-2019) to test the tensile strength at 28d and 180d. The test results of the tensile strength of concrete for each group are shown in Table 4.

[0069] Table 4: Test Results of Tensile Strength of Concrete

[0070]

[0071] It can be seen that the 28d tensile strength of the invention group is 15-20% higher than that of the control group, and the 180d tensile strength of the invention group is 17-20% higher than that of the control group.

[0072] (4) Autogenous Shrinkage Test

[0073] Refer to ASTM C1581 to test the autogenous shrinkage rate of concrete in the early stage (1-7d). The test results of the autogenous shrinkage of concrete for each group are shown in Table 5.

[0074] Table 5: Test Results of Autogenous Shrinkage of Concrete

[0075]

[0076] It can be seen that the self-shrinkage rate of the invention group is reduced by 25-30% compared with the control group.

[0077] (5)Observation of crack development

[0078] The change in crack width within 180 days was monitored by digital image correlation technology (DIC). The concrete crack development results of each group are shown in Table 6.

[0079] Table 6: Concrete crack development results mm

[0080]

[0081] It can be seen that the maximum crack width of the control group reached 0.219-0.300 mm, while the maximum crack width of the invention group was only 0.022-0.050 mm, indicating that the repair efficiency of the invention group was over 85%.

[0082] In summary, when using the functional composite capsule servo fiber for concrete of the present invention to prepare concrete mixtures, the workability, mechanical properties and crack resistance of concrete can be significantly improved, with remarkable technical effects and high promotion and application value.

[0083] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples. The above 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 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, alkali-treat 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 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, 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 at 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 micro-scale cutter, 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 fiber with a diameter of 50 - 200 μm and a length of 10 - 15 mm, degrease it, soak it in 5% NaOH solution for 24 h, then dry it to a constant weight at 60 °C, treat it with KH-550 with a mass fraction of 2% at 60 °C for 1 h, and rinse it with deionized water until neutral after treatment.

3. The preparation method according to claim 1, characterized in that, Adjust the rotation speed of the winding device 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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