Basalt fiber bundle for reinforcing cement concrete and preparation method thereof

Abstract

The invention relates to the technical field of civil engineering materials, and discloses a basalt fiber bundle for reinforcing cement concrete, which comprises the following steps: bundling a plurality of basalt monofilaments to form a fiber bundle body; a regular groove structure is arranged on the surface of the fiber bundle body, and the groove structure is integrally formed through a mold or formed through post-processing; the surface of the fiber bundle body is subjected to sand blasting treatment to form a microcosmic rough layer, and the roughness Ra is 5-15 microns; the surface of the fiber bundle body is coated with a silane coupling agent layer, and chemical bonding is formed between the silane coupling agent layer and the surfaces of the resin matrix and basalt. Through the synergistic effect of the special structure of the fiber surface and surface modification, a mechanical interlocking and chemical bonding dual reinforcement system is formed between the fiber and a matrix. By means of the multi-scale interface design, the load transmission efficiency is remarkably improved, the common interface slippage problem in a traditional reinforcing material is effectively restrained, and the structural integrity is fundamentally improved.

Description

Technical Field

[0001] This invention relates to the field of civil engineering materials technology, and in particular to a basalt fiber bundle for reinforcing cement concrete and its preparation method. Background Technology

[0002] Fiber-reinforced polymer (FRP) composites are key materials for reinforcing concrete structures, and the performance advantages of FRP depend heavily on the interfacial bonding efficiency between the fibers and the matrix. In practical engineering, the interface often becomes a weak link in stress transmission, especially in complex environments such as damp heat and corrosion. Early failure caused by interface deterioration severely restricts the long-term reliability of the reinforcement system, which has become a common technical challenge hindering the widespread application of FRP technology.

[0003] Current technologies primarily improve interfacial properties through two main approaches: physical modification and chemical treatment. Physical methods focus on surface roughening, such as mechanical grooving and sandblasting, to increase mechanical interlocking force and improve bond strength. Chemical methods employ coupling agent coating to establish chemical bonds between fibers and resins. Other techniques attempt to prefabricate regular groove structures on the fiber surface to enhance mechanical interlocking. However, these techniques often employ single modification methods and fail to achieve a synergistic enhancement of physical anchoring and chemical bonding.

[0004] The core flaw in existing technologies lies in the fact that the interface structure formed by traditional surface treatment processes cannot simultaneously achieve both immediate strength and long-term durability. While physical roughening treatments can improve initial bond strength, the surface morphology degrades rapidly under environmental erosion; chemical modification methods, when used alone, easily lead to stress concentration due to a lack of mechanical anchoring support; and post-processed groove structures often damage the integrity of the fiber itself, and their regular geometric shapes cause localized stress peaks. These defects collectively lead to progressive debonding of existing FRP-concrete interfaces under complex working conditions, severely weakening the reinforcement effect. Summary of the Invention

[0005] The purpose of this invention is to provide a basalt fiber bundle for reinforcing cement concrete and its preparation method, which solves the problem that the mechanical anchoring effect and chemical bonding effect caused by the single interface reinforcement method in existing fiber-reinforced materials cannot synergistically improve the instantaneous strength and long-term durability.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A basalt fiber bundle for reinforcing cement concrete, comprising: The fiber bundle body is formed by multiple basalt monofilaments bundled together; The surface of the fiber bundle body is provided with a regular groove structure, which is formed by integral molding or post-processing. The surface of the fiber bundle body is sandblasted to form a micro-rough layer with a roughness Ra of 5 to 15 μm. The fiber bundle body surface is coated with a silane coupling agent layer, which forms a chemical bond with the resin matrix and the basalt surface; The fiber bundle body has variable diameter tapered sections at both ends, and the variable diameter tapered sections are covered with metal sleeves. The inner wall of the metal sleeves has spiral textures with a pitch of 1 to 3 mm and a depth of 0.2 to 0.4 mm, and forms a staggered interlocking with the groove structure.

[0007] Preferably, the groove structure is selected from one of spiral groove, longitudinal groove or mesh groove, the groove depth is 0.3 to 0.5 mm, the width is 0.2 to 0.4 mm, and the spacing between adjacent grooves is 2 to 6 mm.

[0008] Preferably, the sandblasting treatment uses 60-120 mesh quartz sand or alumina sand, the sandblasting pressure is 0.3-0.6 MPa, the sandblasting angle is 70-90°, and the treatment time is 60-90 seconds.

[0009] Preferably, the silane coupling agent is at least one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, with a coating concentration of 2-5 wt%, and is dried at 40-60°C for 15-30 minutes after coating.

[0010] Preferably, the length of the variable-diameter tapered section is 10-30 mm, the diameter gradually changes from the fiber bundle body diameter D to 1.2D-1.5D, and the cone angle is 5-15°; the metal sleeve is made of stainless steel, titanium alloy or nickel-based alloy, and the wall thickness is 0.5-1.2 mm.

[0011] Preferably, an epoxy resin layer is filled between the metal sleeve and the fiber bundle body, the epoxy resin layer containing 10-20 wt% silica nanoparticles, and the curing conditions are 80-120°C for 1-2 hours.

[0012] A method for preparing basalt fiber bundles for reinforcing cement concrete includes the following steps: (1) Basalt melting and drawing: Basalt ore is melted at 1250-1450℃ and drawn into monofilaments with a diameter of 11-17μm through a platinum-rhodium alloy spinneret; (2) Fiber bundling: 400 to 800 monofilaments are bundled together by tension-controlled guide rollers to form fiber bundle raw materials; (3) Resin impregnation: The fiber bundle is impregnated in epoxy resin containing 2-5 wt% silane coupling agent, and the resin viscosity is 300-600 cps; (4) Mold shaping: The impregnated fiber bundle is passed through a mold with grooves on the inner wall. The mold temperature is 60-80℃ and the traction speed is 0.5-2m / min. (5) Heat curing: Curing in sections at 130-160℃ for 30-90 minutes; (6) Surface treatment: The cured fiber bundles are sandblasted and then coated with silane coupling agent solution; (7) End anchoring: A tapered section with varying diameter is processed at both ends of the fiber bundle, a metal sleeve is nested and epoxy resin is injected; (8) End sealing protection: Apply alkali-resistant sealant to the end face of the cut fiber bundle.

[0013] Preferably, the groove of the mold in step (4) is a spiral structure with a pitch of 2 to 6 mm and a depth of 0.3 to 0.5 mm. The matching tolerance between the inner diameter of the mold and the diameter of the fiber bundle is ±0.1 mm.

[0014] Preferably, the silane coupling agent solution in step (6) is coated by atomized spraying or immersion, with a spraying pressure of 0.1 to 0.3 MPa and an immersion time of 15 to 30 minutes.

[0015] Preferably, the thermosetting of step (5) is divided into three stages: First stage: 80-100℃, keep warm for 20-40 minutes to allow the resin to initially crosslink; Second stage: 120-140℃, keep warm for 30-60 minutes to complete the curing of the main body; Third stage: 150-160℃, keep warm for 10-20 minutes.

[0016] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention utilizes the synergistic effect of a special fiber surface structure and surface modification to form a dual reinforcement system between the fiber and the matrix, characterized by mechanical interlocking and chemical bonding. This multi-scale interface design significantly improves load transfer efficiency, effectively suppresses the interfacial slip problem commonly found in traditional reinforcement materials, and fundamentally improves the overall structural integrity.

[0017] 2. The protective system of this invention constructs a dual chemical and physical barrier at the fiber-matrix interface, effectively blocking the penetration of corrosive media such as moisture and ions. This significantly improves the long-term stability of the material in harsh environments, overcoming the insufficient durability of traditional materials due to interface degradation.

[0018] 3. The geometric configuration of this invention achieves a rational distribution of interfacial stress and avoids local stress concentration through a multi-level stress transfer mechanism. This optimization enables the material to exhibit better ductility and failure tolerance under complex loads, significantly improving structural safety performance. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0020] The following is in conjunction with the appendix Figure 1 The present invention will be further described in detail below.

[0021] Example 1: This invention provides a basalt fiber bundle for reinforcing cement concrete and its preparation method, which may include the following steps: Step S1: Preparation and bundling of continuous basalt fibers. Raw material processing: Natural basalt ore with SiO2 content ≥45% and Fe2O3 ≤12% is selected, crushed to a particle size of 5-20mm, and then subjected to magnetic separation (magnetic field strength 0.8T) to remove metal impurities.

[0022] After cleaning, dry at 120℃ for 2 hours, with the moisture content controlled at <0.5%.

[0023] Melt drawing: The raw materials are put into an electric arc furnace and heated to 1350±50℃ at a rate of 10℃ / min. The temperature is held for 1.5 hours to form a homogeneous melt.

[0024] The melt was drawn into wires by a platinum-rhodium alloy spinneret (0.8 mm diameter, 600 holes), with a cooling air temperature of 25℃ and an air velocity of 2 m / s, resulting in a single wire diameter of 13±1 μm.

[0025] Clustering and sorting: The monofilament is guided to the bundler by a ceramic guide wheel (50mm in diameter). The tension of the guide wheel is controlled by a closed-loop servo motor with a fluctuation range of ±0.5N.

[0026] The clusterer uses a honeycomb-shaped filament splitter to ensure that the 600 monofilaments are arranged in parallel with a spacing deviation of less than 5%.

[0027] Step S2: Resin impregnation and mold shaping Resin preparation: Epoxy resin (E-51 type, epoxy value 0.51) and polyamide curing agent (amine value 230) are mixed at a mass ratio of 100:35.

[0028] Add 3 wt% γ-aminopropyltriethoxysilane (KH-550), stir at 500 rpm for 30 minutes, and adjust the viscosity to 450 ± 50 cps after degassing (measured at 25℃).

[0029] Impregnation treatment: The fiber bundle passes through the impregnation tank (2m in length, 30cm in height) at a speed of 1.2m / min, and the resin temperature in the tank is maintained at 40±2℃ by a circulating water bath.

[0030] After impregnation, excess resin is scraped off by two sets of rollers (gap 0.25mm, pressure 0.1MPa), and the coating thickness is controlled at 0.2±0.05mm.

[0031] Mold finalization: After impregnation, the fiber bundle enters a spiral groove mold (made of silicon nitride ceramic) with an inner diameter of 2.5 mm. The groove depth of the inner wall of the mold is 0.4 mm, the pitch is 4 mm, and the lead angle is 30°.

[0032] The mold is divided into three temperature zones: 60℃ at the inlet, 70℃ in the middle, and 65℃ at the outlet. The traction speed is 1.0m / min, and the traction force fluctuation is <2%.

[0033] Step S3: Thermosetting and Cooling Segmented curing: The curing oven is divided into three zones: Zone 1 (preheating): 90±5℃, hold for 30 minutes, heating rate 2℃ / min; Zone 2 (Main Curing): 140±5℃, heat preservation for 50 minutes; Zone 3 (post-curing): 155±5℃, hold for 15 minutes to promote interfacial cross-linking.

[0034] Nitrogen protection is provided inside the furnace, with an oxygen content of <100ppm.

[0035] Cooling and shaping: After curing, the fiber bundle enters the air-cooled tunnel (5m in length), with a wind speed of 3m / s and a temperature gradient that drops from 155℃ to 40℃, with a cooling rate of ≤5℃ / min.

[0036] The winding is pulled and wound up by a tension wheel set (tension 10N), with a winding diameter of 500mm.

[0037] Step S4: Surface Interface Enhancement Treatment Sandblasting: A pneumatic sandblasting machine (pressure 0.5MPa) was used, with 80-mesh white corundum sand (Al2O3≥99%) as the abrasive. The distance between the spray gun and the fiber bundle surface was 100mm, and the moving speed was 10mm / s.

[0038] The surface roughness after sandblasting is Ra = 12 ± 2 μm (measured by a stylus roughness tester).

[0039] Coupling agent coating: The fiber bundle was immersed in a 5wt% KH-550 ethanol solution (pH=5.5) at a temperature of 50±2℃ for 20 minutes.

[0040] After removal, the solution is removed by centrifugation (200 rpm, 30 seconds) and dried with hot air circulation at 60°C for 1 hour.

[0041] Step S5: Construction of end anchoring structure Variable diameter machining: The fiber bundle is heated to 80°C in a 20mm area at both ends using a high-frequency induction heater, and then hot-pressed through a conical mold (half-cone angle 7°) at a pressure of 5MPa for 30 seconds.

[0042] After molding, the diameter of the conical section gradually increases from 2.5mm to 3.2mm, while the continuity of the surface grooves remains intact.

[0043] Nested sleeves: The cylinder is made of 316L stainless steel (wall thickness 0.8mm), and the inner wall is laser-etched with a left-handed spiral texture (pitch 1.5mm, depth 0.3mm).

[0044] Insert the sleeve into the conical section with a gap of 0.1 mm, and pour in epoxy resin containing 15 wt% nano SiO2 (particle size 30 nm) (curing conditions: 80℃ / 1h).

[0045] Step S6: Cutting and sealing Cutting: A fiber laser cutting machine (wavelength 1064nm, power 200W) is used, with a focused spot diameter of 0.1mm, a cutting speed of 10mm / s, and a cut flatness of ≤0.05mm.

[0046] After cutting, use a belt polisher (800 mesh) to treat the end face and remove burrs.

[0047] End cap: Apply alkali-resistant sealant (epoxy-modified silicone resin, viscosity 2000cps) evenly to the end face, with a coating thickness of 0.1mm, and cure at room temperature for 24 hours (humidity ≤60%).

[0048] Example 2: This invention provides a basalt fiber bundle for reinforcing cement concrete and its preparation method, which may include the following steps: Step S1: Preparation and bundling of continuous basalt fibers. Melt drawing: Basalt ore is melted at 1250℃ and drawn into monofilaments with a diameter of 11μm and spinneret orifice diameter of 0.6mm.

[0049] The cooling air velocity for a single filament is 1.5 m / s, and the temperature is 20℃.

[0050] Clustering and sorting: 400 monofilaments are bundled together, the guide wheel tension is 5N, and the spacing deviation is ≤8%.

[0051] Step S2: Resin impregnation and mold shaping Resin preparation: Epoxy resin (E-44 type) is mixed with 12% polyamide curing agent and 2wt% KH-550 is added, resulting in a viscosity of 300cps.

[0052] Mold finalization: The mold inner diameter is 2.2mm, the groove depth is 0.3mm, the pitch is 2mm, the mold temperature is 60℃, and the traction speed is 0.5m / min.

[0053] Step S3: Thermosetting and Cooling Segmented curing: Zone 1: 80℃ / 40 minutes; Zone 2: 120℃ / 90 minutes; Zone 3: 150℃ / 10 minutes.

[0054] Nitrogen and oxygen content <200ppm.

[0055] Cooling: wind speed 2m / s, cooling rate 3℃ / min.

[0056] Step S4: Surface Interface Enhancement Treatment Sandblasting: 60-mesh quartz sand, pressure 0.3 MPa, processing time 60 seconds, roughness Ra = 5 μm.

[0057] Coupling agent coating: Immerse in 2wt% KH-550 solution at 40℃ for 15 minutes, then dry at 50℃ for 1 hour.

[0058] Step S5: Construction of end anchoring structure Variable diameter machining: The tapered section is 10mm long and its diameter gradually increases from 2.2mm to 2.6mm (cone angle 5°), with a pressure of 3MPa.

[0059] Nested sleeves: The sleeve has a 1mm pitch and is filled with 10wt% nano-SiO2 epoxy resin, then cured at 70℃ for 1.5 hours.

[0060] Step S6: Cutting and sealing Cutting: Laser power 150W, speed 8mm / s.

[0061] End sealing: sealant thickness 0.05mm, humidity ≤70%.

[0062] Example 3: This invention provides a basalt fiber bundle for reinforcing cement concrete and its preparation method, which may include the following steps: Step S1: Preparation and bundling of continuous basalt fibers. Melt drawing: Basalt ore is melted at 1450℃ and drawn into monofilaments with a diameter of 17μm and spinneret orifice diameter of 1.0mm.

[0063] The cooling air velocity for a single filament is 3 m / s, and the temperature is 30℃.

[0064] Clustering and sorting: The bundle consists of 800 monofilaments, with a guide wheel tension of 10N and a spacing deviation of ≤3%.

[0065] Step S2: Resin impregnation and mold shaping Resin preparation: Vinyl ester resin (Derakane 411-350) was mixed with 18% MEKP curing agent and 5wt% KH-560 was added, resulting in a viscosity of 600cps.

[0066] Mold finalization: The mold has an inner diameter of 3.0 mm, a groove depth of 0.5 mm, a pitch of 6 mm, a mold temperature of 80℃, and a traction speed of 2 m / min.

[0067] Step S3: Thermosetting and Cooling Segmented curing: Zone 1: 100℃ / 20 minutes; Zone 2: 160℃ / 30 minutes; Zone 3: 160℃ / 20 minutes.

[0068] Nitrogen and oxygen content < 50 ppm.

[0069] Cooling: wind speed 5m / s, cooling rate 7℃ / min.

[0070] Step S4: Surface Interface Enhancement Treatment Sandblasting: 120-mesh silicon carbide sand, pressure 0.6 MPa, processing time 90 seconds, roughness Ra = 15 μm.

[0071] Coupling agent coating: Immerse in 5wt% KH-560 solution at 60℃ for 30 minutes, then dry at 70℃ for 0.5 hours.

[0072] Step S5: Construction of end anchoring structure Variable diameter machining: The tapered section is 30mm long and its diameter gradually increases from 3.0mm to 4.5mm (cone angle 15°), with a pressure of 8MPa.

[0073] Nested sleeves: The sleeve has a 3mm pitch and is filled with 20wt% nano-Al2O3 epoxy resin, then cured at 120℃ for 0.5 hours.

[0074] Step S6: Cutting and sealing Cutting: Laser power 250W, speed 15mm / s.

[0075] End sealing: sealant thickness 0.15mm, humidity ≤50%.

[0076] Comparative Example 1 (mold grooves omitted, integral molding) Compared with Example 1, the difference is that the mold shaping process in step S2 is cancelled, and instead, grooves (depth 0.4mm, pitch 4mm) are machined on the surface of the cured fiber bundle by mechanical grooving. The remaining steps and parameters are the same as in Example 1.

[0077] Comparative Example 2 (sandblasting treatment omitted) Compared with Example 1, the difference is that the sandblasting treatment in step S4 is omitted, and only the coupling agent is coated. The remaining steps and parameters are the same as in Example 1.

[0078] Comparative Example 3 (coupling agent omitted) Compared with Example 1, the difference is that KH-550 coupling agent is not added in the resin preparation of step S2, and the remaining steps and parameters are the same as in Example 1.

[0079] Comparative Example 4 (end anchoring structure omitted) Compared with Example 1, the difference is that the diameter change process and sleeve nesting in step S5 are cancelled, the two ends of the fiber bundle are kept to have the same diameter, and the remaining steps and parameters are the same as in Example 1.

[0080] Test Example 1: Experimental Procedure Instructions 1. Specimen preparation Concrete matrix: C40 ready-mixed concrete, water-cement ratio 0.4, maximum aggregate size 20mm.

[0081] Fiber embedding: The fiber bundle is vertically embedded into the fresh concrete to a depth of 50±1mm.

[0082] Curing conditions: Curing in a standard curing room (20±2℃, RH≥95%) for 28 days.

[0083] 2. Loading scheme Testing equipment: INSTRON 5985 universal testing machine (range 100kN); Loading method: Displacement control mode, loading rate 1mm / min; Clamping method: The upper clamp holds the free end of the fiber bundle, and the lower clamp fixes the concrete test block; 3. Data Collection Data acquisition parameters: Real-time recording of load-displacement curves (sampling frequency 10Hz); Key metrics: Maximum pull-out force F max (kN); Interface slip S (load decreases to 90% F) max Displacement at time (mm).

[0084] Table 1. Results of interfacial bond strength test The experimental results show that the spiral groove structure designed on the fiber bundle surface, combined with the micro-roughened layer formed by sandblasting, significantly enhances the mechanical interlocking effect at the fiber-concrete interface. In the embodiment, the groove structure integrally formed by the mold creates multi-level mechanical interlocking with cement hydration products during the pull-out process, effectively dispersing the interfacial shear stress. In contrast, Comparative Example 1, which uses post-processing grooving, resulted in damage to the fiber monofilaments, inducing stress concentration points, and a decrease in pull-out force of approximately 30%. Furthermore, longitudinal cracking of the fiber was observed in the failure mode, confirming the protective effect of the in-situ molding process on fiber integrity.

[0085] The roughened surface layer (Ra = 5–15 μm) formed by sandblasting generates numerous micromechanical anchoring points in the interface region. Experimental data shows that the slippage in Comparative Example 2, which did not undergo sandblasting, increased by more than 120%, and the damaged interface exhibited a smooth characteristic. This roughening treatment allows cement slurry to penetrate into the micron-level pits on the fiber surface, enhancing anti-slip capability through a physical interlocking mechanism. In the examples, the timing of the sandblasting parameters and coupling agent application further ensured the synergistic effect of chemical bonding and mechanical anchoring.

[0086] The geometry of the grooves on the fiber bundle surface (pitch 2–6 mm, depth 0.3–0.5 mm) guides the cement paste to form a directional crystalline structure. Electron microscopy observation shows that the interface transition zone of the sample in the examples contains a large number of needle-like ettringite crystals. These crystals preferentially grow along the groove direction, forming a three-dimensional interlocking network. In contrast, the mechanical grooving of Comparative Example 1 disrupts the continuity of the resin layer on the fiber surface, resulting in a disordered distribution of the crystalline structure and weakening the synergistic reinforcement effect of this structure. The maximum pull-out force generated in Example 3 due to the optimized groove parameters (pitch 6 mm) in the experimental data verifies the regulatory effect of specific geometric features on the interfacial stress distribution.

[0087] Test Example 2: Experimental Procedure Instructions 1. Specimen preparation Microdroplet sample: Uncured resin droplets (diameter 2.0±0.2mm) are coated on the surface of the fiber bundle and cured to form a coated segment; Positioning and fixing: The fiber bundle is stretched and straightened at both ends using a custom clamp, and the resin droplets are centered to avoid external stress interference; 2. Loading scheme Testing equipment: Favimat+ fiber strength tester (equipped with micro-force sensor, measuring range 50N, accuracy ±0.1N); Loading method: The blade pushes the resin microdroplets at a speed of 0.1 mm / s until the interface detaches; Environmental control: The laboratory temperature is constant at 25±1℃, and the humidity is 50±5%RH; 3. Data Collection Key parameters: Critical deadhesion force F c (N); Interfacial shear strength Where d is the fiber diameter and L is the wrapping length; Damage mode record: Microscopic observation of the interface morphology after debonding (200×); Table 2. Results of resin-fiber interfacial shear strength test Experimental data show that the silane coupling agent premixed in the resin forms a stable chemical bond layer on the fiber surface. In Comparative Example 3, without the addition of coupling agent, the interfacial shear strength decreased by more than 50%, and the damaged interface exhibited a smooth characteristic, confirming that the silanol groups generated by the hydrolysis of the coupling agent undergo a condensation reaction with the hydroxyl groups on the fiber surface, which is the key mechanism for improving interfacial adhesion. The test results of the coupling agent concentration gradient (2-5 wt%) in the examples show that when the concentration reaches 3%, the failure mode changes from interfacial debonding to resin cohesive failure, indicating that the interfacial bonding strength has exceeded the strength of the resin bulk at this point.

[0088] The micron-scale rough structure formed on the fiber surface after sandblasting provides physical anchoring points for resin penetration. In Example 1, a large number of resin fragments remained on the surface of the resin-coated section after debonding. Electron microscopy showed that the resin penetrated into the fiber surface pits to a depth of 5-8 μm, forming a mechanically interlocking structure. In contrast, the smooth interface of Comparative Example 3 caused the resin to adhere only by van der Waals forces, making it prone to overall slippage under shear loads.

[0089] A specific concentration of coupling agent (such as 3 wt% in Example 1) can optimize the wettability of the resin on the fiber surface, with contact angle tests showing a decrease from 72° (without coupling agent) to 28°, significantly improving the resin's ability to spread on the fiber. This improvement allows the resin to fully fill fiber surface defects and form a continuous transition phase during curing, thereby effectively transferring the load to the fiber reinforcement. In Example 3, the excessively high concentration of coupling agent (5 wt%) led to an increase in resin viscosity, which in turn weakened the penetration depth, indicating that the concentration range needs to be dynamically matched with the resin system.

[0090] Test Example 3: Experimental Procedure Instructions 1. Specimen preparation Anchoring specimen: The fiber bundle was anchored at both ends to a C50 concrete substrate (dimensions 150×150×150mm), with an anchoring length of 30mm. Curing conditions: After 28 days of standard curing, dry in a 60℃ oven for 48 hours until constant weight; 2. Loading scheme Testing equipment: MTS370 hydraulic servo fatigue testing machine (maximum load 250kN); Loading mode: Sine wave cyclic load, amplitude 10kN→30kN (stress ratio R=0.33); Frequency 2Hz, number of cycles 10 5 Second-rate Environmental control: Laboratory temperature 23±2℃, humidity 50±5%RH; 3. Data Collection Dynamic monitoring: The end slip is recorded every 5000 cycles (laser displacement sensor, accuracy ±0.01mm); Real-time acquisition of load-displacement curves (sampling frequency 100Hz); Final value test: After the cycle is completed, a monotonic stretch is applied until failure, and the residual pull-out force is recorded. Table 3. End anchorage performance test results The improved interfacial bond strength stems from the synergistic effect of the multi-scale structure on the fiber surface. The integrally molded spiral groove forms a directional stress transfer path in the concrete. Experimental data shows that when the groove depth is 0.3–0.5 mm, the mechanical interlocking effect can increase the pull-out force by more than 25%. Comparative Example 1, where post-processing grooving resulted in damage to the resin layer on the fiber surface, showed microcracks at the groove edges, weakening the interfacial bond between the fiber and resin. This is consistent with the experimental data showing a sharp 30% drop in pull-out force.

[0091] The surface roughness (Ra = 8–12 μm) created by sandblasting improves anti-slip capability by increasing the contact area and mechanical interlocking points. Energy dispersive spectroscopy (EDS) analysis showed that the Ca / Si elemental ratio on the fiber surface increased by 1.8 times after sandblasting, indicating that the sandblasting process promoted heterogeneous nucleation of cement hydration products on the fiber surface. In contrast, the smooth interface of the un-sandblasted sample in Comparative Example 2 resulted in a random distribution of hydration products, failing to form an effective stress transfer network, and its slip amount reached 2.3 times that of the Example group.

[0092] The coupling agent premixing process strengthens the resin-fiber interface transition region through chemical bonding. Infrared spectroscopy detected the sample from the example at 1110 cm⁻¹. -1 The presence of Si-O-Si characteristic peaks confirms that the coupling agent successfully bridged the resin and fiber. This chemical bonding increased the interfacial shear strength from 12 MPa in Comparative Example 3 to over 25 MPa, and the failure mode changed from interfacial debonding to resin cohesive failure, indicating that the interfacial bonding strength has exceeded the resin bulk strength.

[0093] Test Example 4: Experimental Procedure Instructions 1. Specimen pretreatment Solution preparation: Saturated Ca(OH)₂ solution (pH = 13.5 ± 0.2), add 0.1 mol / L NaOH to maintain alkalinity; Immersion conditions: The specimen is completely immersed in the solution, and the sealed container is placed in a constant temperature water bath at 40±1℃; Sampling cycle: Take 3 sets of parallel samples every 7 days, rinse with distilled water and test immediately; 2. Performance Testing Test equipment: Pull-out test: Shimadzu AG-X100kN testing machine; Microscopic observation: Hitachi SU8010 field emission electron microscope; Test process: After soaking, the sample was placed in a drying oven at 25°C for 24 hours. Perform a pull-out test (loading rate 1 mm / min); Energy dispersive spectroscopy (EDS) was performed on the interface region. 3. Data Collection Key parameters: Strength retention rate (F0 is the initial strength, F) t (Strength after soaking); Changes in the content of interfacial elements (Ca / Si atomic ratio); Failure mode record: macroscopic failure morphology + microscopic crack observation; Table 4. Results of Alkali Resistance Environmental Performance Tests The silane coupling agent continues to exert its chemical stabilizing effect in an alkaline environment. The silanol groups produced by its hydrolysis form an alkali-resistant Si-O-Si bond network with the hydroxyl groups on the fiber surface. In Example 1, the Ca / Si atomic ratio at the interface remained above 1.2 after 28 days of immersion, indicating that the coupling agent effectively blocked OH groups. - The erosion of the fiber-resin interface was observed. In contrast, in Comparative Example 3, the sample without coupling agent showed a large amount of Ca(OH)2 crystals (Ca / Si ratio of 4.7) at the interface. The expansion stress of these crystals caused the resin layer to bubble and fall off, and the strength retention rate dropped to below 55%.

[0094] The rough surface structure (Ra = 8–12 μm) formed by sandblasting enhances corrosion resistance by extending the solution penetration path. Micro-CT scans showed that the micro-pit depth of the fiber surface in Example 1 reached 15–20 μm, requiring alkaline solutions to flow around it for penetration, resulting in a penetration rate reduction of more than 60% compared to the smooth surface of Comparative Example 2. This structure causes the corrosion front to be discontinuously distributed, delaying the overall deterioration process of the interfacial transition zone.

[0095] End-sealing treatment prevents alkaline media from penetrating along the fiber bundle axially through a physical isolation mechanism. In Example 1, after the sample ends were sealed with epoxy resin, no OH was detected in the end region during a 28-day test. - Concentration gradient change. In contrast, the unsealed sample of Comparative Example 2 showed a reduction in diameter of the end fiber monofilament (approximately 12%), and energy dispersive spectroscopy analysis showed a 28% decrease in Si content in this region, confirming that the end-sealing treatment effectively cut off the migration channel of the corrosive medium.

[0096] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A basalt fiber bundle for reinforcing cement concrete, characterized in that, include: The fiber bundle body is formed by multiple basalt monofilaments bundled together; The surface of the fiber bundle body is provided with a regular groove structure, which is formed by integral molding or post-processing. The surface of the fiber bundle body is sandblasted to form a micro-rough layer with a roughness Ra of 5 to 15 μm. The fiber bundle body surface is coated with a silane coupling agent layer, which forms a chemical bond with the resin matrix and the basalt surface; The fiber bundle body has variable diameter tapered sections at both ends, and the variable diameter tapered sections are covered with metal sleeves. The inner wall of the metal sleeves has spiral textures with a pitch of 1 to 3 mm and a depth of 0.2 to 0.4 mm, and forms a staggered interlocking with the groove structure.

2. The basalt fiber bundle for reinforcing cement concrete according to claim 1, characterized in that, The groove structure is selected from one of spiral grooves, longitudinal grooves or mesh grooves, with a groove depth of 0.3 to 0.5 mm, a width of 0.2 to 0.4 mm, and a spacing of 2 to 6 mm between adjacent grooves.

3. The basalt fiber bundle for reinforcing cement concrete according to claim 1, characterized in that, The sandblasting treatment uses 60-120 mesh quartz sand or alumina sand, with a sandblasting pressure of 0.3-0.6 MPa, a sandblasting angle of 70-90°, and a treatment time of 60-90 seconds.

4. The basalt fiber bundle for reinforcing cement concrete according to claim 1, characterized in that, The silane coupling agent is at least one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, with a coating concentration of 2-5 wt%, and is dried at 40-60°C for 15-30 minutes after coating.

5. A basalt fiber bundle for reinforcing cement concrete according to claim 1, characterized in that, The length of the variable-diameter tapered section is 10-30 mm, the diameter gradually changes from the fiber bundle body diameter D to 1.2D-1.5D, and the cone angle is 5-15°; the metal sleeve is made of stainless steel, titanium alloy or nickel-based alloy, and the wall thickness is 0.5-1.2 mm.

6. A basalt fiber bundle for reinforcing cement concrete according to claim 1, characterized in that, An epoxy resin layer is filled between the metal sleeve and the fiber bundle body. The epoxy resin layer contains 10-20 wt% silica nanoparticles and is cured at 80-120°C for 1-2 hours.

7. A method for preparing basalt fiber bundles for reinforcing cement concrete, comprising a basalt fiber bundle for reinforcing cement concrete according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Basalt melting and drawing: Basalt ore is melted at 1250-1450℃ and drawn into monofilaments with a diameter of 11-17μm through a platinum-rhodium alloy spinneret; (2) Fiber bundling: 400 to 800 monofilaments are bundled together by tension-controlled guide rollers to form fiber bundle raw materials; (3) Resin impregnation: The fiber bundle is impregnated in epoxy resin containing 2-5 wt% silane coupling agent, and the resin viscosity is 300-600 cps; (4) Mold shaping: The impregnated fiber bundle is passed through a mold with grooves on the inner wall. The mold temperature is 60-80℃ and the traction speed is 0.5-2m / min. (5) Heat curing: Curing in sections at 130-160℃ for 30-90 minutes; (6) Surface treatment: The cured fiber bundles are sandblasted and then coated with silane coupling agent solution; (7) End anchoring: A tapered section with varying diameter is machined at both ends of the fiber bundle, a metal sleeve is nested in it and epoxy resin is injected; (8) End sealing protection: Apply alkali-resistant sealant to the end face of the cut fiber bundle.

8. A method for preparing basalt fiber bundles for reinforcing cement concrete according to claim 7, characterized in that, The groove of the mold in step (4) has a spiral structure with a pitch of 2 to 6 mm and a depth of 0.3 to 0.5 mm. The matching tolerance between the inner diameter of the mold and the diameter of the fiber bundle is ±0.1 mm.

9. A method for preparing basalt fiber bundles for reinforcing cement concrete according to claim 7, characterized in that, The silane coupling agent solution described in step (6) is coated by atomized spraying or immersion, with a spraying pressure of 0.1 to 0.3 MPa and an immersion time of 15 to 30 minutes.

10. A method for preparing basalt fiber bundles for reinforcing cement concrete according to claim 7, characterized in that, The thermosetting process in step (5) consists of three stages: First stage: 80-100℃, keep warm for 20-40 minutes to allow the resin to initially crosslink; Second stage: 120-140℃, keep warm for 30-60 minutes to complete the curing of the main body; Third stage: 150-160℃, keep warm for 10-20 minutes.

Images