Sodium alginate-nano calcium carbonate composite modified basalt fiber and preparation method and application thereof

Abstract

The application provides a sodium alginate-nano calcium carbonate composite modified basalt fiber and a preparation method and application thereof, and belongs to the technical field of building materials and fiber surface modification.The preparation method comprises four steps of fiber glue removal pretreatment, sodium alginate / nano calcium carbonate mixed slurry preparation, calcium chloride crosslinking liquid preparation and immersion crosslinking film forming.The instant crosslinking characteristics between the sodium alginate polymer chain and calcium ions are utilized to generate a tough calcium alginate hydrogel film in situ on the surface of the chopped basalt fiber, and the nano calcium carbonate is physically blocked in the three-dimensional gel network.The preparation process is carried out in pure water phase at room temperature, and the toxic organic solvent and high-temperature reaction are abandoned, so that the process is extremely simple, green and environmentally-friendly, and the production cycle is short.

Description

Technical Field

[0001] This invention belongs to the field of building materials and fiber surface modification technology, and particularly relates to a sodium alginate-nano calcium carbonate composite modified basalt fiber, its preparation method and application. Background Technology

[0002] Basalt fiber (BF), a novel inorganic, environmentally friendly, and high-performance fiber, possesses excellent properties such as high tensile strength, corrosion resistance, and high-temperature resistance, and is widely used in reinforcing cement-based and polymer resin-based composite materials. However, untreated basalt fibers have a relatively smooth surface and strong chemical inertness, resulting in weak interfacial mechanical and chemical bonding forces between them and the matrix material. Under stress, the fibers are prone to slipping and being pulled out of the matrix, failing to fully realize their high-strength reinforcing effect.

[0003] Currently, surface modification of basalt fibers often employs chemical grafting with silane coupling agents (such as KH-560) or physical coating with nanomaterials (such as nano-SiO2, carbon nanotubes, etc.). However, traditional silane modification processes are complex, often involving the use of organic solvents, which can easily cause environmental pollution. Simple nanoparticle impregnation methods, on the other hand, are prone to secondary agglomeration of nanoparticles in alkaline cement environments, exhibiting weak adhesion to the fiber surface and easily peeling off over large areas during stirring and stress, resulting in unstable modification effects. Therefore, developing a simple, environmentally friendly fiber surface composite modification technology that effectively prevents nanoparticle agglomeration and shedding has significant engineering practical value. Summary of the Invention

[0004] To address the technical problems of complex modification processes, easy agglomeration and peeling of nanoparticles in existing technologies, this invention proposes a sodium alginate-nano calcium carbonate composite modified basalt fiber, its preparation method, and its application.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing sodium alginate-nano calcium carbonate composite modified basalt fiber, comprising the following steps: (1) The short-cut basalt fibers were pretreated to remove glue, and the pretreated bare fibers were obtained; (2) Sodium alginate (SA) is dissolved in water to form sodium alginate initial solution; nano calcium carbonate is dispersed by ultrasonication and then mixed into the sodium alginate initial solution, and stirred evenly to obtain a mixed slurry of sodium alginate and nano calcium carbonate. (3) The pretreated bare fiber described in step (1) is immersed in the mixed slurry obtained in step (2) and then the fiber after slurry is immersed in calcium chloride aqueous solution for cross-linking reaction, so that sodium alginate and calcium ions undergo instantaneous cross-linking reaction, and a three-dimensional alginate gel network coating with nano calcium carbonate is generated in situ on the fiber surface, thus obtaining the sodium alginate-nano calcium carbonate composite modified basalt fiber.

[0006] Further, in step (1), the degumming pretreatment involves immersing the chopped basalt fibers in anhydrous ethanol or acetone for ultrasonic cleaning, followed by rinsing with water and drying to obtain the pretreated bare fibers.

[0007] Furthermore, in step (2), the mass concentration of sodium alginate in the mixed slurry is 1%~2%.

[0008] Furthermore, in step (2), the amount of nano-calcium carbonate used is 10% to 20% of the mass of sodium alginate.

[0009] Further, in step (2), the initial sodium alginate solution is obtained by dissolving sodium alginate in water and stirring it in a water bath at 50°C for 1-2 hours.

[0010] Furthermore, in step (3), the mass concentration of the calcium chloride aqueous solution is 3% to 5%.

[0011] Furthermore, in step (3), the crosslinking reaction takes 30 minutes.

[0012] This invention also proposes a sodium alginate-nano calcium carbonate composite modified basalt fiber prepared according to the above preparation method.

[0013] This invention also proposes the application of the above-mentioned sodium alginate-nano calcium carbonate composite modified basalt fiber in fiber-reinforced cement-based composite materials.

[0014] Furthermore, based on the total volume of the fiber-reinforced cementitious composite material after final hardening, the volume content of the sodium alginate-nano-calcium carbonate composite modified basalt fiber is 0.3%.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: (1) This invention improves the adhesion stability of nanoparticles on the fiber surface, effectively preventing aggregation and detachment. This invention utilizes a three-dimensional gel network formed by the cross-linking of sodium alginate and calcium ions to encapsulate and fix nano-calcium carbonate particles within the network. During subsequent drying and shrinkage, the gel layer forms a dense coating on the basalt fiber surface. This physical encapsulation structure effectively overcomes the technical defects of traditional simple physical impregnation methods, where nanoparticles adhere solely to van der Waals forces and are easily peeled off during concrete mixing, achieving uniform loading and stable fixation of nanomaterials on the fiber surface.

[0016] (2) This invention improves the interfacial transition zone structure between the fiber and the cement matrix, playing a dual role of stress buffering and nucleation induction. The modified calcium alginate film, as a flexible transition layer, can absorb part of the strain energy at the crack tip when the composite material cracks under load, thus playing a mechanical buffering role; at the same time, the nano-calcium carbonate on the surface of the coating layer, as a hydration nucleus, can promote the nucleation and dense growth of cement hydration products (such as CSH gel) on the fiber surface. This mechanism effectively enhances the mechanical interlocking force and interfacial bonding strength between the fiber and the cement matrix.

[0017] (3) This invention improves the macroscopic mechanical properties of composite materials and reduces matrix brittleness. Based on the above-mentioned improvement in interface structure, modified basalt fibers can generate greater interfacial friction and energy dissipation during the pull-out process. Incorporating them into matrices such as high-strength cementitious materials can effectively improve the ultimate flexural strength of composite materials and significantly reduce the compression-flexural ratio. This method effectively improves the brittle fracture tendency of high-strength concrete and enhances the overall toughness and deformation capacity of the material. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The images are SEM images of sodium alginate-nano calcium carbonate composite modified basalt fibers at different magnifications in Example 1. The scale bar for (a) is 10 μm, and the scale bar for (b) is 5 μm. Figure 2 SEM images of raw short-cut basalt fibers at different magnifications, (a) with a scale bar of 50 μm and (b) with a scale bar of 1 μm; Figure 3 The energy spectrum of sodium alginate-nano calcium carbonate composite modified basalt fiber in Example 1 is shown. Figure 4 The energy spectrum of the original short-cut basalt fibers; Figure 5The infrared spectra of the fibers in Example 1 (sodium alginate-nano calcium carbonate composite modified basalt fiber), Comparative Example 2 (original short-cut basalt fiber), Comparative Example 3 (sodium alginate modified basalt fiber) and Comparative Example 4 (nano calcium carbonate modified basalt fiber) are shown, where (a) is the Fourier transform infrared full wavenumber spectrum and (b) is a comparison of the stacked Fourier transform infrared spectra of the characteristic functional group regions. Detailed Implementation

[0019] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0020] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0021] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0022] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0023] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0024] This invention provides a method for preparing sodium alginate-nano calcium carbonate composite modified basalt fiber, comprising the following steps: (1) The short-cut basalt fibers were pretreated to remove glue, and the pretreated bare fibers were obtained; (2) Sodium alginate (SA) is dissolved in water to form sodium alginate initial solution; nano calcium carbonate is dispersed by ultrasonication and then mixed into sodium alginate initial solution, stirred evenly to obtain a mixed slurry of sodium alginate and nano calcium carbonate. (3) The exposed fibers pretreated in step (1) are immersed in the mixed slurry obtained in step (2) and then the slurryed fibers are immersed in calcium chloride aqueous solution for cross-linking reaction, so that sodium alginate and calcium ions undergo instantaneous cross-linking reaction, and a three-dimensional alginate gel network coating with nano-calcium carbonate is generated in situ on the fiber surface, thus obtaining sodium alginate-nano-calcium carbonate composite modified basalt fiber.

[0025] In step (1) of the preferred embodiment of the present invention, the degumming pretreatment involves immersing the short-cut basalt fibers in anhydrous ethanol or acetone for ultrasonic cleaning, followed by rinsing with water and drying to obtain pretreated bare fibers.

[0026] In step (2) of the preferred embodiment of the present invention, the mass concentration of sodium alginate in the mixed slurry is 1%~2%.

[0027] In step (2) of the preferred embodiment of the present invention, the amount of nano-calcium carbonate used is 10% to 20% of the mass of sodium alginate.

[0028] In step (2) of the preferred embodiment of the present invention, the initial sodium alginate solution is obtained by stirring for 1-2 hours under a water bath at 50°C.

[0029] In step (3) of the preferred embodiment of the present invention, the mass concentration of the calcium chloride aqueous solution is 3%~5%.

[0030] In step (3) of the preferred embodiment of the present invention, the crosslinking reaction time is 30 min.

[0031] For example, the preparation method of sodium alginate-nano calcium carbonate composite modified basalt fiber in this embodiment of the invention specifically includes the following steps: (1) Fiber surface degumming pretreatment: The short basalt fibers were immersed in anhydrous ethanol or acetone for ultrasonic cleaning for 30 minutes to remove the original sizing agent; then rinsed with deionized water and dried at 60°C to obtain the pretreated bare fibers. (2) Preparation of SA / CaCO3 mixed slurry: Dissolve sodium alginate (SA) powder in a portion of deionized water and stir at 50°C for 1-2 hours until the solution is completely dissolved and transparent to obtain sodium alginate initial solution; take 10%-20% of the sodium alginate powder mass of nano-calcium carbonate powder, add the nano-calcium carbonate powder to the remaining deionized water, and disperse it by strong ultrasonication for 30 minutes to completely disperse it to obtain nano-calcium carbonate suspension; then pour the nano-calcium carbonate suspension into the sodium alginate initial solution and stir mechanically for 1 hour to obtain milky white SA / CaCO3 mixed slurry; wherein, by strictly controlling the total amount of deionized water used to dissolve sodium alginate and disperse nano-calcium carbonate, the mass concentration of sodium alginate in the final mixed slurry is 1.0%-2.0%; (3) Preparation of crosslinking agent solution: Dissolve anhydrous calcium chloride (CaCl2) in deionized water to prepare a calcium chloride aqueous solution with a mass concentration of 3.0%~5.0%, and keep it at room temperature for later use; (4) Impregnation and cross-linking: The pretreated bare fiber obtained in step (1) is put into the SA / CaCO3 mixed slurry in step (2) and gently stirred at room temperature to coat the fiber; then the coated fiber is taken out and quickly immersed in the calcium chloride aqueous solution in step (3) for instantaneous cross-linking reaction; after taking it out, it is washed with water to remove free ions and dried in a drying oven at 60℃ to constant weight. During the drying process, the calcium alginate gel layer shrinks in volume and forms a dense coating layer on the fiber surface, thus obtaining sodium alginate-nano calcium carbonate composite modified basalt fiber.

[0032] This invention also proposes a sodium alginate-nano calcium carbonate composite modified basalt fiber prepared according to the above preparation method.

[0033] This invention also proposes an application of the above-mentioned sodium alginate-nano-calcium carbonate composite modified basalt fiber in fiber-reinforced cementitious composite materials.

[0034] In a preferred embodiment of the present invention, the volume content of sodium alginate-nano-calcium carbonate composite modified basalt fiber is 0.3% based on the total volume of the fiber-reinforced cementitious composite material after final hardening.

[0035] In a preferred embodiment of the present invention, the reference mix proportion parameters of the fiber-reinforced cementitious composite material are: water-cement ratio of 0.30 and mortar-cement ratio of 1:1.5; the dry materials include cement (PO 42.5 grade ordinary Portland cement), fly ash (Grade I fly ash), mineral powder (S95 mineral powder) and standard sand (ISO standard sand), wherein the cementing materials are cement, fly ash and mineral powder.

[0036] All raw materials used in the embodiments of this invention were purchased commercially.

[0037] In this embodiment of the invention, "room temperature" refers to "25±2℃".

[0038] The technical solution of the present invention will be further illustrated by the following embodiments.

[0039] Example 1 (1) Fiber surface degumming pretreatment: Short basalt fibers (12 mm in length) are immersed in anhydrous ethanol or acetone for ultrasonic cleaning for 30 min to remove the original sizing agent; then rinsed with deionized water and dried at 60°C to obtain the pretreated bare fibers. (2) Preparation of SA / CaCO3 mixed slurry: Sodium alginate (SA) powder was dissolved in deionized water and stirred in a 50°C water bath for 1.5 h until the solution was completely dissolved and transparent to obtain sodium alginate initial solution; another 10% of sodium alginate powder was nano-calcium carbonate powder, which was added to deionized water and ultrasonically dispersed for 30 min by a 300W probe to obtain nano-calcium carbonate suspension; then the nano-calcium carbonate suspension was poured into sodium alginate initial solution and mechanically stirred for 1 h to obtain milky white SA / CaCO3 mixed slurry (the volume ratio of deionized water used to prepare sodium alginate initial solution to that used to prepare nano-calcium carbonate suspension was 4:1. By strictly controlling the total amount of deionized water used to prepare initial solution and suspension, the mass concentration of sodium alginate in the final SA / CaCO3 mixed slurry reached 1.5%). (3) Preparation of crosslinking agent solution: Dissolve anhydrous calcium chloride (CaCl2) in deionized water to prepare a calcium chloride aqueous solution with a mass concentration of 4% and keep it at room temperature for later use; (4) Impregnation and cross-linking: The pretreated bare fiber obtained in step (1) is put into the SA / CaCO3 mixed slurry in step (2) and gently stirred at room temperature to coat the fiber; then the coated fiber is taken out and quickly immersed in the calcium chloride aqueous solution in step (3) for instantaneous cross-linking reaction for 30 min; after taking it out, it is washed with water 3 times to remove free ions and dried in a drying oven at 60℃ to constant weight. During the drying process, the calcium alginate gel layer shrinks in volume and forms a dense coating layer on the fiber surface, thus obtaining sodium alginate-nano calcium carbonate composite modified basalt fiber; (5) Prepare materials according to the mass ratio of cement: fly ash: mineral powder: standard sand: water: water-reducing agent (polycarboxylate high-efficiency water-reducing agent, solid content 20%) = 520: 80: 200: 1200: 240: 8.0. First, mix cement, fly ash, mineral powder and standard sand. Then, evenly sprinkle in sodium alginate-nano calcium carbonate composite modified basalt fiber (the amount added is 0.3% of the total volume of the fiber-reinforced cement-based composite material). Dry mix for 90 seconds. Finally, add water and water-reducing agent and stir at high speed to form the fiber-reinforced cement-based composite material.

[0040] Example 2 Same as Example 1, except that step (2) is different, as follows: Sodium alginate (SA) powder was dissolved in deionized water and stirred in a 50°C water bath for 1.5 hours until the solution was completely dissolved and transparent, yielding a primary sodium alginate solution. Separately, 20% (by weight of the sodium alginate powder) of nano-calcium carbonate powder was added to deionized water and ultrasonically dispersed for 30 minutes using a 300W probe to obtain a nano-calcium carbonate suspension. This nano-calcium carbonate suspension was then poured into the primary sodium alginate solution and mechanically stirred for 1 hour to obtain a milky-white SA / CaCO3 mixed slurry (the volume ratio of deionized water used to prepare the primary sodium alginate solution to that used to prepare the nano-calcium carbonate suspension was 4:1; by strictly controlling the total amount of deionized water used in preparing the primary solution and the suspension, the final SA / CaCO3 mixed slurry achieved a sodium alginate concentration of 2.0%). The remaining steps were consistent with Example 1.

[0041] Comparative Example 1 Prepare the materials according to the mass ratio of cement: fly ash: mineral powder: standard sand: water: water-reducing agent (polycarboxylate high-efficiency water-reducing agent, solid content 20%) = 520: 80: 200: 1200: 240: 8.0. First, mix the cement, fly ash, mineral powder and standard sand, dry mix for 90 seconds, and finally add water and water-reducing agent and mix at high speed to form a cement-based composite material.

[0042] Comparative Example 2 Same as Example 1, except that the sodium alginate-nano calcium carbonate composite modified basalt fiber is replaced with short-cut basalt fiber of equal volume.

[0043] Comparative Example 3 Same as Example 1, except that the modification is done with pure sodium alginate, specifically including the following steps: (1) Fiber surface degumming pretreatment: The short basalt fibers were immersed in anhydrous ethanol or acetone for ultrasonic cleaning for 30 minutes to remove the original sizing agent; then rinsed with deionized water and dried at 60°C to obtain the pretreated bare fibers. (2) Dissolve sodium alginate (SA) powder in deionized water and stir at 50°C for 1.5 h until the solution is completely dissolved and transparent to obtain a sodium alginate solution with a mass concentration of 1.5%. (3) Preparation of crosslinking agent solution: Dissolve anhydrous calcium chloride (CaCl2) in deionized water to prepare a calcium chloride aqueous solution with a mass concentration of 4% and keep it at room temperature for later use; (4) Impregnation and cross-linking: The pretreated bare fiber obtained in step (1) is put into the sodium alginate solution in step (2) and gently stirred at room temperature to coat the fiber; then the coated fiber is taken out and quickly immersed in the calcium chloride aqueous solution in step (3) for instantaneous cross-linking reaction for 30 min; after taking it out, it is washed with water 3 times to remove free ions and dried in a drying oven at 60℃ to constant weight. During the drying process, the calcium alginate gel layer shrinks in volume and forms a dense coating layer on the fiber surface, thus obtaining sodium alginate modified basalt fiber; (5) Prepare materials according to the mass ratio of cement: fly ash: mineral powder: standard sand: water: water-reducing agent (polycarboxylate high-efficiency water-reducing agent, solid content 20%) = 520: 80: 200: 1200: 240: 8.0. First, mix cement, fly ash, mineral powder and standard sand. Then, evenly sprinkle in sodium alginate modified basalt fiber (the amount added is 0.3% of the total volume of the fiber-reinforced cement-based composite material finally prepared). Dry mix for 90 seconds. Finally, add water and water-reducing agent and stir at high speed to form the cement-based composite material.

[0044] Comparative Example 4 Same as Example 1, except that the physical modification of single-nano calcium carbonate includes the following steps: (1) Fiber surface degumming pretreatment: The short basalt fibers were immersed in anhydrous ethanol or acetone for ultrasonic cleaning for 30 minutes to remove the original sizing agent; then rinsed with deionized water and dried at 60°C to obtain the pretreated bare fibers. (2) Add nano-calcium carbonate powder to deionized water and disperse it by ultrasonication with a 300W probe for 30 minutes to completely disperse it and obtain a nano-calcium carbonate suspension with a mass concentration of 0.15% (the mixed slurry in Example 1 contains 1.5% sodium alginate, while nano-calcium carbonate accounts for 10% of sodium alginate, so the equivalent mass concentration of nano-calcium carbonate in the final slurry system is 0.15%). (3) Preparation of crosslinking agent solution: Dissolve anhydrous calcium chloride (CaCl2) in deionized water to prepare a calcium chloride aqueous solution with a mass concentration of 4% and keep it at room temperature for later use; (4) Impregnation and cross-linking: The pretreated bare fiber obtained in step (1) is put into the nano calcium carbonate suspension in step (2) and gently stirred at room temperature to coat the fiber; then the coated fiber is taken out and quickly immersed in the calcium chloride aqueous solution in step (3) for curing reaction, the reaction time is 30 min; after taking it out, it is washed with water 3 times to remove free ions and dried in a drying oven at 60℃ to constant weight to obtain nano calcium carbonate modified basalt fiber; (5) Prepare materials according to the mass ratio of cement: fly ash: mineral powder: standard sand: water: water-reducing agent (polycarboxylate high-efficiency water-reducing agent, solid content 20%) = 520: 80: 200: 1200: 240: 8.0. First, mix cement, fly ash, mineral powder and standard sand. Then, evenly sprinkle nano-calcium carbonate modified basalt fiber (the amount added is 0.3% of the total volume of the fiber-reinforced cement-based composite material finally prepared). Dry mix for 90 seconds. Finally, add water and water-reducing agent and stir at high speed to form the cement-based composite material.

[0045] Performance testing (1) Mechanical property testing The cement-based composite materials of the examples and comparative examples were tested for compressive strength, flexural strength, compression-flexural ratio (to evaluate brittleness), and autogenous shrinkage rate at 28 days. The results are summarized in Table 1.

[0046] Table 1. Performance test results of cement-based composite materials in the examples and comparative examples. In terms of macroscopic mechanical properties, the optimal embodiment of the present invention (Example 1) achieved a 28-day compressive strength of 70.4 MPa and a flexural strength of 11.6 MPa, respectively, which were 17.1% and 17.2% higher than the blank reference group (Comparative Example 1), and were comprehensively superior to the single-modification control group (Comparative Examples 3 and 4). The above-mentioned strength improvement verifies the positive synergistic effect of surface modification. In the compressive-flexural ratio index for evaluating material toughness, the system directly incorporating untreated fibers (Comparative Example 2) showed a deteriorated compressive-flexural ratio to 6.406 due to weak interfaces, exhibiting more significant brittle fracture characteristics; while Example 1, while achieving peak strength, significantly reduced the compressive-flexural ratio from 6.406 to 6.069, maintaining it at a level slightly better than the blank reference group (Comparative Example 1), demonstrating an effective synergistic effect of strengthening and toughening. In the evaluation of volume stability, the 0.30 low water-cement ratio matrix easily induces severe self-drying shrinkage (e.g., the self-shrinkage rate of Comparative Example 1 is as high as 5.85 × 10⁻⁶). -4 Embodiment 1 of the present invention exhibits excellent crack-resistant and shrinkage-controlling performance, significantly limiting its self-shrinkage rate to 3.86 × 10⁻⁶. -4 The relative decrease was 34% compared to the benchmark group.

[0047] (2) Analysis of microstructure and modification mechanism The morphology of the original short-cut basalt fibers and the sodium alginate-nano calcium carbonate composite modified basalt fibers obtained in Example 1 were compared and analyzed by scanning electron microscopy (SEM).

[0048] Figure 1The images are SEM images of sodium alginate-nano-calcium carbonate composite modified basalt fibers at different magnifications in Example 1 (the scale bar for (a) is 10 μm, and the scale bar for (b) is 5 μm). Figure 2 The SEM images of the raw, short-cut basalt fibers at different magnifications (scale bar for (a) is 50 μm, and for (b) it is 1 μm) show that the surface of the untreated raw, short-cut basalt fibers exhibits an extremely smooth, flat cylindrical structure with almost no adhering substances or microtexture. This typical chemical inertness and physical smoothness makes it difficult for the fibers to form effective mechanical interlocking with hydration products (such as CSH gel) after being incorporated into cement-based materials. Once the matrix is ​​stretched and cracked, the fibers are prone to "smooth pull-out" failure, which directly explains the high compression-flexural ratio (6.406) and increased brittleness of the material in Comparative Example 2. In contrast, the sodium alginate-nano-calcium carbonate composite modified basalt fibers exhibit a multi-scale rough structure. In their low- and medium-magnification morphologies, it can be observed that the surface of the basalt fibers is coated with a dense polymer film. Its microscopic modification mechanism lies in the fact that sodium alginate (SA) macromolecular chains contain a large number of carboxyl and hydroxyl groups. When the sized fibers are immersed in calcium chloride (CaCl2) solution, the Ca in the solution... 2+ It will quickly replace the sodium in sodium alginate. + The calcium carbonate nanoparticles undergo efficient ionic crosslinking with carboxyl oxygen atoms on adjacent polymer chains, forming a three-dimensional network structure that solidifies in situ into a water-insoluble calcium alginate gel network. During this process, the nano-calcium carbonate particles in the slurry are trapped within the gel and micropores by this three-dimensional network, preventing self-aggregation of the nanoparticles. After drying and dehydration, the gel network undergoes volume shrinkage, ultimately solidifying on the fiber surface into a rough inorganic-organic composite network coating. This multi-scale rough configuration not only significantly enhances the mechanical anchoring effect between the fiber and the cement matrix, but the nano-calcium carbonate and gel network on its surface also act as hydration nuclei, inducing and promoting the nucleation and enrichment of cement hydration products (such as CSH gel) in the interfacial transition zone (ITZ), thereby improving the shear strength of the composite material.

[0049] (3) Surface chemical composition evolution analysis To further confirm the successful grafting of the composite modified layer onto the basalt fiber surface and the chemical evolution process, X-ray energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were performed on the surfaces of each sample. Table 2 shows the comparison of EDS elemental mass fractions on the surfaces of the original chopped basalt fibers and the sodium alginate-nano calcium carbonate composite modified basalt fibers obtained in Example 1. Figure 3 The image shows the energy dispersive spectroscopy (EDS) spectrum of the sodium alginate-nano calcium carbonate composite modified basalt fiber in Example 1. Figure 4 This is the energy spectrum of the original short-cut basalt fibers.

[0050] Table 2 Comparison of surface EDS element mass fraction Combine Table 2 and Figure 3 , Figure 4 It can be seen that the unmodified fiber surface mainly contained matrix elements such as Si (21.86%), Al (7.20%), and Mg (3.41%), derived from the basalt mineral framework. However, the surface elemental composition of the fiber after modification with sodium alginate-nano-calcium carbonate composites changed. Due to the synergistic introduction of sodium alginate organic polymer chains and nano-calcium carbonate, the surface C element content increased from 13.65% in the baseline group to 22.50%. The most crucial chemical evidence lies in the increase in the mass fraction of Ca from the original 5.96% to 15.80%, confirming the presence of Ca. 2+ The large consumption of crosslinking agent and the high-density enrichment of nano-CaCO3 particles on the fiber surface led to a significant dilution of the signals of Si, Al, and Mg elements in the inner fiber layer within the detection depth due to the dense physical shielding formed by the modified composite coating on the fiber substrate. Specifically, the Si content decreased significantly to 14.50%. Furthermore, the presence of Na in the crosslinking reaction further contributed to this dilution. + by Ca 2+ After thorough replacement and leaching by water, the residual amount of Na on the fiber surface in Example 1 was extremely low (only 0.50%), which confirmed the thoroughness of the crosslinking replacement reaction from the perspective of elemental abundance.

[0051] The infrared spectra of the fibers in Example 1 (sodium alginate-nano-calcium carbonate composite modified basalt fiber), Comparative Example 2 (original chopped basalt fiber), Comparative Example 3 (sodium alginate modified basalt fiber), and Comparative Example 4 (nano-calcium carbonate modified basalt fiber) are shown below. Figure 5 (a) is the Fourier transform infrared full-wavenumber spectrum, and (b) is a comparison of the Fourier transform infrared spectra of stacked characteristic functional group regions. The peak shape evolution of the infrared spectral curves provides a more direct chemical verification from the perspective of molecular functional group configuration. It can be seen that the untreated fiber in Comparative Example 2 only reaches a peak shape of 1080 cm⁻¹. -1 The vicinity exhibits strong characteristic peaks of inorganic Si-O-Si bond asymmetric stretching vibrations. However, in the spectrum of the composite modified fiber (Example 1), not only at 3400 cm⁻¹... -1 A broad -OH stretching vibration band appeared at this point due to the introduction of hydrophilic groups from sodium alginate, and the characteristic framework peak of calcite-type CaCO3 was fully displayed in the low wavenumber region: 875 cm⁻¹. -1 The out-of-plane bending vibration peak at 713 cm⁻¹ and the in-plane bending vibration peak at 713 cm⁻¹ are highly consistent with the surge in Ca in EDS.

[0052] In summary, the synergistic effect of microstructure, quantitative elemental evolution, and molecular bond energy transfer demonstrates that this invention has successfully constructed a calcium alginate-nano calcium carbonate composite modified layer on the surface of basalt fibers, which possesses both high chemical stability and micro / nano roughness.

[0053] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing sodium alginate-nano-calcium carbonate composite modified basalt fiber, characterized in that, Includes the following steps: (1) The short-cut basalt fibers were pretreated to remove glue, and the pretreated bare fibers were obtained; (2) Sodium alginate is dissolved in water to form sodium alginate initial solution; nano calcium carbonate is dispersed by ultrasonication and then mixed into the sodium alginate initial solution, and stirred evenly to obtain a mixed slurry of sodium alginate and nano calcium carbonate. (3) The pretreated bare fiber described in step (1) is immersed in the mixed slurry obtained in step (2) and then the fiber after slurry is immersed in calcium chloride aqueous solution for cross-linking reaction to obtain the sodium alginate-nano calcium carbonate composite modified basalt fiber.

2. The preparation method of sodium alginate-nano-calcium carbonate composite modified basalt fiber according to claim 1, characterized in that, In step (1), the degumming pretreatment involves immersing the chopped basalt fibers in anhydrous ethanol or acetone for ultrasonic cleaning, followed by rinsing with water and drying to obtain the pretreated bare fibers.

3. The preparation method of sodium alginate-nano-calcium carbonate composite modified basalt fiber according to claim 1, characterized in that, In step (2), the mass concentration of sodium alginate in the mixed slurry is 1%~2%.

4. The preparation method of sodium alginate-nano-calcium carbonate composite modified basalt fiber according to claim 1, characterized in that, In step (2), the amount of nano-calcium carbonate used is 10% to 20% of the mass of sodium alginate.

5. The preparation method of sodium alginate-nano-calcium carbonate composite modified basalt fiber according to claim 1, characterized in that, In step (2), the initial sodium alginate solution is obtained by dissolving sodium alginate in water and stirring it in a water bath at 50°C for 1-2 hours.

6. The preparation method of sodium alginate-nano-calcium carbonate composite modified basalt fiber according to claim 1, characterized in that, In step (3), the mass concentration of the calcium chloride aqueous solution is 3% to 5%.

7. The preparation method of sodium alginate-nano-calcium carbonate composite modified basalt fiber according to claim 1, characterized in that, In step (3), the cross-linking reaction takes 30 minutes.

8. A sodium alginate-nano calcium carbonate composite modified basalt fiber prepared by the preparation method according to any one of claims 1 to 7.

9. The application of sodium alginate-nano-calcium carbonate composite modified basalt fiber as described in claim 8 in fiber-reinforced cementitious composite materials.

10. The application of sodium alginate-nano-calcium carbonate composite modified basalt fiber according to claim 9 in fiber-reinforced cementitious composite materials, characterized in that, The volume content of the sodium alginate-nano-calcium carbonate composite modified basalt fiber is 0.3% based on the total volume of the fiber-reinforced cementitious composite material after final hardening.

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