Water reducer modified basalt fiber reinforced cement concrete and preparation method thereof

Abstract

The invention discloses a water reducing agent modified basalt fiber reinforced cement concrete and a preparation method thereof, and belongs to the technical field of material and traffic crossing. The preparation method comprises the following steps: firstly, synthesizing a water reducing agent containing carboxyl, amino and a polyether side chain, and carrying out surface chemical grafting modification on basalt fibers subjected to alkali liquor hydroxylation treatment by using the water reducing agent to obtain modified basalt fibers; during concrete preparation, the modified basalt fiber is added into a concrete dry material according to a specific volume mixing amount to be dispersed, and the water reducing agent dry material is further doped during wet mixing. Through dual application of the water reducing agent in fiber modification and concrete compounding, the interface bonding force between the fiber and a cement matrix and the dispersity of the fiber in concrete are synergistically improved, and the problem that the workability and the mechanical property of the concrete are difficult to consider at the same time under the condition of high mixing amount of the basalt fiber is solved; the strength and durability of the concrete are remarkably improved while excellent construction fluidity is guaranteed, and the engineering application range of the concrete is expanded.

Description

Technical Field

[0001] This invention relates to the fields of organic and inorganic non-metallic materials and transportation cross-technology, specifically to a water-reducing agent modified basalt fiber reinforced cement concrete and its preparation method. Background Technology

[0002] Basalt fiber (BF) is an inorganic high-performance fiber made from natural basalt through high-temperature melting and drawing. In highway concrete engineering, basalt fiber offers multiple advantages, including mechanical reinforcement, improved durability, environmental friendliness, and cost-effectiveness, effectively enhancing the crack resistance, toughness, and long-term service performance of concrete. However, its application faces two key technical bottlenecks: First, the smooth and chemically inert surface of the fiber results in weak physical and chemical bonding with cementitious materials, making the interface a weak point with low stress transfer efficiency. This hinders the full realization of the fiber's reinforcing and toughening potential and may even lead to localized stress concentration due to interface defects. Second, when the volumetric content of basalt fiber exceeds 0.3%, the fibers tend to entangle and clump together during mixing, significantly increasing the viscosity and internal friction of the concrete mixture, leading to a sharp decline in workability. Studies have shown that when the fiber content reaches 0.5%, the slump of concrete can decrease by more than 30%, which seriously affects the pumping, pouring and compaction performance of concrete, and is particularly unfavorable for engineering applications with high requirements for construction performance, such as high-flowability pavement concrete and pumped concrete.

[0003] To enhance the interfacial bond between basalt fibers and the cement matrix and improve the mechanical properties of concrete, researchers have developed various surface modification techniques. For example, a multi-step treatment of basalt fibers involves oxidation with hydrogen, followed by etching with hydrochloric acid, and finally modification with a nano-silica coating. This method significantly enhances the interfacial bond between the fibers and the concrete matrix (existing technology CN120271293A). Alternatively, the fibers can be acid-etched first, followed by secondary modification with nano-silica liquid, and then combined with natural sand modified with water glass solution as fine aggregate, resulting in concrete with high early strength and excellent freeze-thaw resistance (existing technology CN119797825A). Another technique involves preparing a calcium carbonate / PEI / PAMAM composite slurry, then impregnating pretreated hydrochloric acid-treated fibers into this slurry to complete the modification, significantly improving the crack resistance and compressive strength of concrete (existing technology CN117819836A). In addition, there are methods to disperse basalt fibers in an ethanol solution containing tetraethoxysilane, form an amorphous silica layer on the fiber surface through hydrolysis, and then anchor the basalt fiber powder to improve its dispersibility and alkali resistance in concrete (previous technology CN119080418A); or to first graft the fibers with a vinyl silane coupling agent, and then graft water-absorbing resin onto the fiber surface through an addition reaction to improve compatibility and use the water-retaining function of the resin to inhibit early cracking of concrete (previous technology CN116199481A).

[0004] In summary, existing technologies primarily improve the compatibility and interfacial forces of basalt fibers with the cement matrix by controlling the surface morphology (roughness), chemical activity (hydrophilicity), or introducing functional coatings. These methods do indeed enhance the mechanical properties of concrete to some extent. However, these modification methods generally fail to effectively address the deterioration of concrete rheological properties caused by increased fiber content; that is, the workability and constructability of concrete significantly decrease with high fiber content. This greatly limits the widespread application of basalt fiber reinforced concrete in modern engineering projects requiring good pumpability, high fluidity, and rapid construction. Therefore, developing a new technology that can simultaneously optimize the mechanical properties and workability of basalt fiber reinforced concrete remains a key challenge that urgently needs to be overcome in this field.

[0005] Therefore, to address the aforementioned problems, this invention provides a water-reducing agent-modified basalt fiber reinforced cement concrete and its preparation method. By designing and synthesizing a novel water-reducing agent, and using this water-reducing agent to perform surface chemical grafting modification on basalt fibers, the modified fibers not only significantly improve the interfacial adhesion between the modified fibers and the cement matrix in the concrete, but also effectively improve the rheological properties of the concrete under high fiber content due to their inherent dispersion and lubrication effects. This synergistically achieves simultaneous optimization of reinforcement effect and construction performance, providing an effective technical solution for expanding the application range of basalt fiber reinforced concrete. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies in which basalt fiber reinforced cement concrete cannot simultaneously achieve high mechanical properties and good workability. It provides a water-reducing agent modified basalt fiber reinforced cement concrete and its preparation method. This technical solution designs and synthesizes a water-reducing agent with a specific structure and uses it to covalently and ionicly modify the surface of basalt fibers. This allows the modified fibers to be uniformly dispersed even at high dosages and significantly improves the interfacial bonding and workability of the concrete matrix, thereby synergistically improving the strength and workability of the concrete.

[0007] The objective of this invention is achieved through the following technical solution: A water-reducing agent-modified basalt fiber-reinforced cement concrete comprises cement, admixtures, coarse aggregate, fine aggregate, water, and modified basalt fiber in proportions according to concrete design specifications; the modified basalt fiber is prepared through the following steps: (1) Preparation of water-reducing agent: The water-reducing agent is a copolymer containing carboxyl groups, amino groups and polyether side chains synthesized by free radical polymerization and ring-opening grafting reaction. Its preparation process includes: (1a) Methacrylic acid, methylene succinic acid and glycerol carbonate methacrylate are dissolved in water in a molar ratio of 4:2:2 to form a solution with a monomer concentration of 5-10 wt%. 0.15-5% of the total molar amount of 3-mercaptopropionic acid is added as a chain transfer agent to obtain solution A. Ammonium persulfate is prepared into a 5 wt% aqueous solution to obtain solution B, wherein the amount of ammonium persulfate is 1.5-3 wt% of the total mass of the monomer. Solution B is added dropwise to solution A under stirring in an ice bath, and the temperature is raised to 80°C and reacted for 4 hours to obtain glycerol carbonate methacrylate copolymer solution C. (1b) Prepare a 5wt% aqueous solution D of methoxy polyethylene glycolamine, add solution C to solution D, wherein the molar ratio of glycerol carbonate methacrylate copolymer to methoxy polyethylene glycolamine is 1:1.2, react under nitrogen protection for 24 hours, and then add 30wt% NaOH solution to adjust to neutrality to obtain the water-reducing agent; (2) Surface modification of basalt fibers: (2a) Disperse basalt short fibers (4~12mm) in NaOH or KOH alkaline solution with a concentration of 0.5~5mol / L, with a mass ratio of basalt fiber to alkaline solution of 1:10. Stir at 300rpm for 10~60 minutes at room temperature to 80℃, filter, wash with water until neutral, and vacuum dry at 60~100℃ to obtain hydroxylated basalt fibers; (2b) The water-reducing agent obtained in step (1), the hydroxylated basalt fiber obtained in step (2a) and the metal salt catalyst are dispersed in water at a mass ratio of 2:10:0.1 to form a mixture with a solid content of 10wt%. The mixture is stirred at 80℃ and 300rpm for 2 hours, then stirred at room temperature for 20 minutes, filtered and dried to obtain water-reducing agent modified basalt fiber.

[0008] Preferably, the volumetric dosage of the modified basalt fiber in concrete is 0.1% to 1.2%. The introduction of this modified fiber, through the steric hindrance and lubrication effect of the water-reducing agent molecules chemically grafted onto its surface, effectively solves the problems of fiber agglomeration and increased concrete viscosity under high filling amounts. Simultaneously, through the tight bonding of strongly polar groups such as carboxyl and amino groups with cement hydration products, it significantly enhances the fiber-matrix interfacial force, achieving a balance between reinforcement effect and workability.

[0009] Preferably, in step (1b), the methoxy polyethylene glycol amine has a molecular weight of 1000-3000. Polyether amines in this molecular weight range can provide suitable steric hindrance, ensuring the extension of the water-reducing agent molecular chains to effectively disperse cement particles and fibers, while avoiding entanglement that may be caused by excessively long molecular chains.

[0010] Preferably, in step (2b), the metal salt catalyst is selected from at least one of tetrabutyl titanate or zinc acetate. Such catalysts can promote the esterification reaction or formation of coordination bonds between the active groups in the water-reducing agent molecule (such as the hydroxyl groups after ring opening of cyclic carbonates from glycerol carbonate methacrylate) and the hydroxyl groups on the surface of basalt fibers, thereby achieving a strong chemical grafting.

[0011] Preferably, during concrete mixing, an antifoaming agent and an aqueous solution of the water-reducing agent are also added; the dosage of the water-reducing agent is 0.3~0.8 wt% of the concrete solid content; the dosage of the antifoaming agent is 0.02~0.05 wt% of the concrete solid content. The water-reducing agent is used here as a compound admixture, producing a "homogeneous synergistic effect" with the same type of water-reducing agent molecules already grafted onto the fiber surface. This allows for more efficient adsorption onto cement particles and the incompletely covered fiber surface, thereby further optimizing the fluidity and slump retention of the entire concrete system. The addition of the antifoaming agent eliminates harmful air bubbles generated by fiber introduction and high-speed mixing, ensuring the final density and strength of the concrete.

[0012] This application also claims a method for preparing the above-mentioned water-reducing agent modified basalt fiber reinforced cement concrete, comprising the following steps: S1. Preparation of pretreated fibers: Prepare the water-reducing agent modified basalt fibers according to steps (1) and (2); S2. Dry mixing: Put cement, admixtures, coarse aggregate, and fine aggregate into a forced mixer and dry mix for 1-2 minutes until evenly mixed; S3. Fiber dispersion: Slowly add the modified basalt fiber obtained in step S1 into the mixer and continue to dry mix for 2-3 minutes to make the fiber evenly dispersed in the dry material; S4. Wet mixing and molding: Add mixing water, water-reducing agent solution and defoamer to the mixer, and wet mix for 3-5 minutes to obtain concrete mixture; wherein the water-cement ratio is 0.35-0.45; S5. Pouring and curing: Pour the mixture into the mold, vibrate to compact it, cover to keep it moist, let it stand for 12-24 hours, then remove it from the mold and carry out standard curing.

[0013] Preferably, this method, through a specific feeding and mixing sequence of "dry mixing first, then wet mixing" combined with forced mixing, ensures that the modified basalt fiber is highly uniformly dispersed in the concrete, avoiding fiber clumping, which is the foundation for achieving high-performance concrete.

[0014] Preferably, the concrete mixture in step S4 has a slump of 120-160 mm, a spread of ≥500 mm, and no visible fiber clumping or bleeding. These workability indicators demonstrate that even with a high fiber content, the concrete still exhibits excellent fluidity and anti-segregation properties, fully meeting the requirements for pumping construction and road paving.

[0015] Preferably, a twin-shaft forced mixer is used for mixing in steps S2 to S4. Compared to a gravity mixer, the twin-shaft forced mixer has stronger shear force, which can more effectively break up fiber clumps and achieve uniform mixing of fibers with dry and wet materials. It is a key piece of equipment to ensure the homogeneity of high-fiber concrete.

[0016] Preferably, in step S5, an immersion vibrator is used for compaction at a frequency of 12,000 times per minute, with each vibration point lasting 20-30 seconds, until the concrete surface shows signs of slurry and no air bubbles overflow. Sufficient vibration ensures the compactness of the concrete, allowing the modified fibers to bond more tightly to the matrix and fully exert their reinforcing effect.

[0017] Preferably, the modified basalt fiber in step S3 is added at a rate of 0.1% to 1.2% of the concrete volume, and concentrated addition of the fiber should be avoided. Using a slow and uniform addition method helps the fiber to pre-disperse in the dry material, reducing the burden of subsequent mixing and preventing localized agglomeration.

[0018] This application also claims the application of a water-reducing agent in the surface modification of basalt fibers, wherein the water-reducing agent is a copolymer containing carboxyl, amino, and polyether side chains prepared in step (1) above; its first use is as an interface modifier, grafted onto the surface of hydroxylated basalt fibers through chemical bonding; its second use is as a water-reducing component in concrete mixing, directly added to the concrete mixture. This application uses the water-reducing agent as an interface modifier, anchoring it to the fiber surface through chemical methods, giving the fiber the dual functions of "self-dispersibility" and "strong adhesion", thereby fundamentally solving the long-standing contradiction in the field of basalt fiber reinforced concrete where reinforcement and plasticization are difficult to achieve simultaneously. When the volumetric content of the modified basalt fiber in concrete reaches a high filling level of 0.5% to 1.2%, the concrete can still maintain good workability (slump not less than 120mm), and its 28-day compressive strength can be increased by more than 15% compared with concrete using unmodified fibers, showing significant comprehensive performance advantages.

[0019] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This invention synergistically optimizes and enhances the construction performance by using a special water-reducing agent to perform surface grafting modification on basalt fibers. The modified fibers have both strong interfacial bonding and self-dispersing functions, which can significantly improve the concrete strength at high dosages (≤1.2%) while maintaining excellent fluidity and pumpability, thus completely solving the fundamental contradiction in traditional technologies where it is difficult to balance the enhancement effect and construction performance. 2. This invention achieves uniform dispersion and interface strengthening. Through the "alkali activation-chemical grafting" modification process and a specific stirring procedure, it ensures that the fiber is highly uniformly dispersed in the concrete and avoids agglomeration. The grafted polar groups form a strong bond with the cement hydration products, which greatly strengthens the fiber-matrix interface and optimizes stress transfer efficiency. 3. The present invention has a simplified process and is environmentally friendly. The modification process is carried out in an aqueous solution under mild conditions, without the need for complex equipment or organic solvents. It simplifies the traditional multi-step processing flow, is green and efficient, and is easy to apply on a large scale. 4. This invention improves workability and stability. The modified fiber and the compound water-reducing agent work synergistically to enable concrete to maintain excellent workability (slump 120~160mm, spread ≥500mm) even with high fiber content, while improving density and long-term volume stability. 5. This invention breaks through the limitation of fiber content on workability, provides a reliable solution for the preparation of high-performance fiber concrete, and strongly promotes its large-scale application in high-end fields such as highways, long-span bridges, high-rise buildings and protective engineering. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, some of the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can be made based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the water-reducing agent in Embodiment 1 of the present invention. Detailed Implementation

[0022] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail.

[0023] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0024] Example 1 See appendix Figure 1 This embodiment provides a method for preparing water-reducing agent modified basalt fiber reinforced cement concrete, including the following steps: S1. Synthesis of water-reducing agent: (1) Dissolve methacrylic acid, methylene succinic acid and glycerol carbonate methacrylate in distilled water at a molar ratio of 4:2:2 to form a solution with a monomer concentration of 8wt%; add 3-mercaptopropionic acid as a chain transfer agent at a molar ratio of 2.0% of the total monomer to obtain solution A.

[0025] (2) Dissolve 2.0% of the total mass of ammonium persulfate in water to prepare a 5wt% aqueous solution to obtain solution B.

[0026] (3) Under ice bath stirring, solution B was slowly added dropwise to solution A; after the addition was completed, the temperature was raised to 80°C and the reaction was continued for 4 hours to obtain glycerol carbonate methacrylate copolymer solution C.

[0027] (4) Prepare a 5wt% aqueous solution D of methoxy polyethylene glycolamine with a molecular weight of 2000; add solution C to solution D, wherein the molar ratio of glycerol carbonate methacrylate copolymer to methoxy polyethylene glycolamine is 1:1.2; react at room temperature for 24 hours under nitrogen protection.

[0028] (5) Add 30wt% NaOH solution to the reaction solution to adjust to neutrality; concentrate the solution under reduced pressure at 60℃, and then spray dry to obtain the water-reducing agent dry material.

[0029] S2. Surface modification of basalt fiber: (1) Prepare a 2 mol / L NaOH alkaline solution; disperse 12 mm long basalt short chopped fibers in the alkaline solution at a mass ratio of 1:10; treat for 30 minutes under mechanical stirring at 60℃ and 300 rpm.

[0030] (2) After the reaction, filter and rinse repeatedly with deionized water until neutral; place the fiber in an 80°C vacuum oven and dry for 4 hours to obtain hydroxylated basalt fiber.

[0031] (3) Take 5g of the above-mentioned water-reducing agent dry material, disperse it in deionized water, and prepare a 20wt% aqueous solution; take 10g of the solution, and disperse it together with 50g of hydroxylated basalt fiber and 0.5g of tetrabutyl titanate in deionized water to form a mixed suspension with a solid content of 10wt%.

[0032] (4) Place the suspension in an 80°C water bath and stir at 300 rpm for 2 hours, then stir at room temperature for 20 minutes.

[0033] (5) Filter and collect the fibers, wash with deionized water, and vacuum dry at 80°C to obtain water-reducing agent modified basalt fibers.

[0034] S3. Preparation of water-reducing agent modified basalt fiber reinforced cement concrete: Concrete reference mix proportion (kg / m³) 3 The ingredients are: P.O42.5 cement 400, Grade II fly ash 100, fine aggregate (medium sand) 700, coarse aggregate (5~25mm continuous graded crushed stone) 1050, water 185 (water-cement ratio 0.37).

[0035] (1) Put cement, fly ash, fine aggregate and coarse aggregate into a twin-shaft forced mixer and dry mix for 1.5 minutes until they are evenly mixed.

[0036] (2) Slowly add the modified basalt fiber prepared in step S2, controlling the final volumetric content to 0.8% (approximately 21.6 kg / m³). 3 Continue dry mixing for 2.5 minutes to ensure the fibers are evenly dispersed in the dry material.

[0037] (3) Add mixing water, water-reducing agent accounting for 0.6 wt% of the concrete solid content and polyether defoamer accounting for 0.03 wt% of the concrete solid content to the mixer; wet mix for 4 minutes to obtain concrete mixture; the measured slump of the mixture is 145 mm, the spread is 540 mm, and there is no fiber clumping or water bleeding.

[0038] (4) Pour the mixture into 100mm×100mm×100mm and 100mm×100mm×400mm test molds, and use an immersion vibrator (frequency 12000 times / min) to vibrate point by point for 25 seconds at each point until the surface is covered with slurry and there are no air bubbles.

[0039] (5) Cover with plastic film to keep moist, let stand at room temperature (20±2℃) for 24 hours, then demold and move to a standard curing room (temperature 20±2℃, relative humidity ≥95%) to cure until the specified age.

[0040] Example 2 This embodiment is based on the above embodiment 1, and the similarities with the above embodiment 1 will not be repeated.

[0041] The difference from Example 1 above lies in the following: the dry content of the water-reducing agent and the amount of fiber modifier: In step S2 (surface modification of basalt fibers), the mass ratio of water-reducing agent, hydroxylated basalt fibers, and tetrabutyl titanate catalyst is adjusted to 1:10:0.1, that is, the amount of water-reducing agent is halved. In step S3 (concrete preparation), the dry content of the water-reducing agent is adjusted to 0.4 wt% of the solid content of the concrete, and the volumetric content of the modified basalt fibers is adjusted to 0.5%.

[0042] Example 3 This embodiment is based on the above embodiment 1, and the similarities with the above embodiment 1 will not be repeated.

[0043] The difference from Example 1 above lies in the following: Regarding the raw materials and dosage of each component in the water-reducing agent synthesis: In step S1 (synthesis of the water-reducing agent), the molecular weight of methoxy polyethylene glycol amine is changed to 1500. In step S3 (concrete preparation), the dosage of the water-reducing agent is adjusted to 0.8%, and the volumetric dosage of modified basalt fiber is increased to 1.2%.

[0044] Comparative Example 1 This comparative example is based on Example 1 above, and the similarities with Example 1 above will not be repeated.

[0045] The difference from Example 1 above is as follows: Fiber type: In step 3 (concrete preparation), the basalt fibers modified in step S2 are not used; instead, untreated raw basalt fibers (12 mm in length) with an equal volume fraction (0.8%) are used directly. The water-reducing agent content remains at 0.6%.

[0046] Comparative Example 2 This comparative example is based on Example 1 above, and the similarities with Example 1 above will not be repeated.

[0047] The difference from Example 1 above lies in the following: fiber type and water-reducing agent adjustment: In step S3 (concrete preparation), untreated raw basalt fibers (0.8% admixture) were used. To achieve an initial slump similar to that of Example 1 (approximately 145 mm), the dry admixture dosage of the water-reducing agent was increased to 1.2 wt% of the concrete solids content, while the defoamer dosage was increased to 0.05%. The wet mixing time was extended to 6 minutes to improve dispersion.

[0048] Comparative Example 3 This comparative example utilizes existing technology, employing a traditional acid etching combined with a nano-silica coating method to modify basalt fibers, aiming to enhance their interfacial adhesion with the cement matrix. The specific steps are as follows: (1) Basalt fibers of the same specification (length 12mm) were immersed in a 10wt% hydrochloric acid solution and stirred at 60°C for 30 minutes to etch the fiber surface and increase its roughness.

[0049] (2) Take out the fiber, rinse it repeatedly with deionized water until neutral, and then dry it in an oven at 80°C.

[0050] (3) Immerse the dried fiber in a commercially available aqueous dispersion of nano silica (5wt% solid content) and soak it at room temperature for 1 hour to allow the nano silica particles to deposit and adhere to the fiber surface.

[0051] (4) Take out the fiber and dry it at 100°C for 2 hours to obtain basalt fiber modified by acid etching and nano silica coating.

[0052] (5) The modified fiber was added at a volume ratio of 0.8% and a conventional polycarboxylate superplasticizer at a mass ratio of 0.6% of the total mass of cementitious materials. The concrete was mixed, molded, cured and tested in accordance with the concrete mix proportion and preparation steps (including the order of feeding, mixing parameters, molding and curing conditions) described in Example 1.

[0053] The concrete mixtures prepared in the above embodiments and comparative examples were subjected to workability tests. The molded specimens were cured for 7 days and 28 days, respectively, and their compressive strength and flexural strength were tested. The test data are shown in Table 1.

[0054] Table 1

[0055] As shown in Table 1, regarding the synergistic optimization of workability and mechanical properties, the concrete prepared using the method of this invention (Examples 1-3) exhibits excellent workability (slump 130-158 mm, spread ≥ 510 mm) and significant enhancement in mechanical properties (28-day compressive strength 58.1-65.3 MPa, flexural strength 7.1-8.2 MPa) within the fiber content range of 0.5%-1.2%. This verifies that the dual strategy of surface modification of fibers through water-reducing agents and their use as admixtures can effectively synergistically improve the workability and load-bearing capacity of high-fiber-content concrete.

[0056] Advantages of the modification method of this invention: Comparing Example 1 with Comparative Example 1 (using unmodified fiber) and Comparative Example 3 (using conventional modified fiber + commercial water-reducing agent), it can be found that, under the same fiber content (0.8%) and similar water-reducing agent content, the modification method provided by this invention (Example 1) has significant advantages in workability and 28-day strength (compressive strength is 3.6~6.4 MPa higher). This indicates that the molecular design of the water-reducing agent of this invention and the strategy of using "fiber modification-system compounding" are of the same origin, and are more effective in improving interfacial adhesion and ensuring dispersion flowability.

[0057] Regarding performance at high fiber content: In Example 3, the workability still met the pumping requirements (slump 130mm) at a high fiber content of 1.2%, and the mechanical properties reached their maximum, proving the strong adaptability and effectiveness of the method of the present invention for high-filling systems.

[0058] In comparison with traditional methods: Comparative Example 2 attempted to improve the workability of the unmodified fiber system by significantly increasing the dosage of the water-reducing agent of this invention (1.2%). Although the slump was similar, the strength improvement was limited and the economic efficiency was poor. This highlights the necessity of surface modification of the fibers; simply increasing the water-reducing agent cannot fundamentally solve the problems of weak interfaces and high viscosity.

[0059] The test methods for the above performance tests are as follows: Slump and spread: Tests were conducted according to the People's Republic of China National Standard "Test Methods for Performance of Ordinary Concrete Mixtures" (GB / T50080-2016). Fresh concrete mixture was placed into a slump cone in three layers, each layer tamped 25 times. After smoothing, the cone was lifted vertically, and the height difference between the highest point of the slumped concrete mixture and the top of the cone was measured; this is the slump (unit: mm). Subsequently, the maximum diameter of the slumped mixture in two mutually perpendicular directions was measured with a steel ruler, and the average value was taken as the spread (unit: mm).

[0060] Mechanical property testing: Compressive strength: Tested according to the People's Republic of China National Standard "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081-2019). 100mm×100mm×100mm cube specimens cured to the specified age (7 days, 28 days) were placed in the center of the pressure plate of a compression testing machine and continuously and uniformly loaded at a loading rate of 0.5MPa / s to 0.8MPa / s until specimen failure. The maximum load was recorded. The compressive strength was calculated using the following formula, with the result accurate to 0.1MPa: ƒ_c = F / A; where ƒ_c is the compressive strength of the concrete cube (MPa), F is the failure load (N), and A is the bearing area of ​​the specimen (mm²). 2 The arithmetic mean of the three test specimens was taken as the compressive strength value of the group of specimens.

[0061] Flexural strength: Tested according to GB / T50081-2019. A 100mm×100mm×400mm prism specimen cured to 28 days of age was subjected to a three-point bending test on a universal testing machine, with a 300mm distance between the two supports. The loading point was located at the midpoint of the specimen's span. A continuous and uniform loading rate of 0.05MPa / s to 0.08MPa / s was applied until the specimen fractured, and the failure load was recorded. The flexural strength was calculated using the following formula, with the result accurate to 0.01MPa: ƒ_f=(F×l) / (b×h 2 ); where ƒ_f is the flexural strength of concrete (MPa), F is the failure load (N), l is the support spacing (mm), b is the specimen cross-sectional width (mm), and h is the specimen cross-sectional height (mm). The arithmetic mean of the three specimen measurements is taken as the flexural strength value of the group of specimens.

[0062] Fiber dispersibility observation: After wet mixing and before pouring, visually observe the fresh concrete mixture for any visible fiber agglomeration or bundle formation, and record the observations. Simultaneously, after specimen failure, observe the fiber distribution and pull-out phenomena on the fracture surface as supplementary evidence for qualitative evaluation of fiber dispersibility and interfacial bonding.

[0063] All tests were conducted in a standard laboratory environment (temperature 20±2℃, relative humidity 50%±10%) to ensure the reliability and comparability of the test results.

[0064] In summary, this invention, by designing and synthesizing a water-reducing agent with a specific structure and using it as both a surface modifier for basalt fibers and an admixture in concrete mixing, fundamentally solves the contradiction between high strength and high workability in traditional basalt fiber concrete. At a volumetric admixture of up to 1.2%, the modified fibers, thanks to their self-dispersing and strong interfacial bonding properties, not only significantly improve the mechanical properties of concrete (28-day compressive and flexural strengths increased by approximately 18% and 24% respectively compared to the unmodified system), but also synergistically ensure excellent workability (slump ≥130mm, spread ≥510mm), achieving simultaneous optimization of reinforcement and workability. Furthermore, the modification method provided by this invention is green, efficient, and simple, laying a solid technical foundation for the large-scale application of basalt fibers in high-end concrete engineering.

[0065] The embodiments described above merely illustrate more specific and detailed implementations of the present invention, and should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A water-reducing agent modified basalt fiber-reinforced cement concrete, characterized in that, It includes cement, admixtures, coarse aggregate, fine aggregate, water, and modified basalt fiber in proportions according to concrete design specifications; the modified basalt fiber is prepared through the following steps: (1) Preparation of water-reducing agent: The water-reducing agent is a copolymer containing carboxyl groups, amino groups and polyether side chains synthesized by free radical polymerization and ring-opening grafting reaction. Its preparation process includes: (1a) Methacrylic acid, methylene succinic acid and glycerol carbonate methacrylate are dissolved in water in a molar ratio of 4:2:2 to form a solution with a monomer concentration of 5-10 wt%. 0.15-5% of the total molar amount of 3-mercaptopropionic acid is added as a chain transfer agent to obtain solution A. Ammonium persulfate is prepared into a 5 wt% aqueous solution to obtain solution B, wherein the amount of ammonium persulfate is 1.5-3 wt% of the total mass of the monomer. Solution B is added dropwise to solution A under stirring in an ice bath, and the temperature is raised to 80°C and reacted for 4 hours to obtain glycerol carbonate methacrylate copolymer solution C. (1b) Prepare a 5wt% aqueous solution D of methoxy polyethylene glycolamine, add solution C to solution D, wherein the molar ratio of glycerol carbonate methacrylate copolymer to methoxy polyethylene glycolamine is 1:1.2, react under nitrogen protection for 24 hours, and then add 30wt% NaOH solution to adjust to neutrality to obtain the water-reducing agent; (2) Surface modification of basalt fibers: (2a) Disperse 4-12 mm basalt short fibers in NaOH or KOH alkaline solution with a concentration of 0.5-5 mol / L, with a mass ratio of basalt fiber to alkaline solution of 1:

10. Stir at 300 rpm for 10-60 minutes at room temperature to 80°C, filter, wash with water until neutral, and vacuum dry at 60-100°C to obtain hydroxylated basalt fibers; (2b) The water-reducing agent obtained in step (1), the hydroxylated basalt fiber obtained in step (2a) and the metal salt catalyst are dispersed in water at a mass ratio of 2:10:0.1 to form a mixed aqueous dispersion with a solid content of 10wt%. The mixture is stirred at 80℃ and 300rpm for 2 hours, then stirred at room temperature for 20 minutes, filtered and dried to obtain water-reducing agent modified basalt fiber. The volumetric dosage of the modified basalt fiber in concrete is 0.1% to 1.2%.

2. The water-reducing agent-modified basalt fiber-reinforced cement concrete according to claim 1, characterized in that, In step (1b), the molecular weight of the methoxy polyethylene glycolamine is 1000~3000.

3. The water-reducing agent-modified basalt fiber-reinforced cement concrete according to claim 1, characterized in that, In step (2b), the metal salt catalyst is selected from at least one of tetrabutyl titanate or zinc acetate.

4. The water-reducing agent-modified basalt fiber-reinforced cement concrete according to claim 1, characterized in that, During concrete mixing, defoamer and a water-reducing agent aqueous solution with a concentration of 5~20wt% are also added; the dosage of the water-reducing agent is 0.3~0.8wt% of the solid content of the concrete; the dosage of the defoamer is 0.02~0.05wt% of the solid content of the concrete.

5. A method for preparing water-reducing agent-modified basalt fiber-reinforced cement concrete according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Preparation of pretreated fibers: Prepare the water-reducing agent modified basalt fibers according to steps (1) and (2) in claim 1; S2. Dry mixing: Put cement, admixtures, coarse aggregate, and fine aggregate into a forced mixer and dry mix for 1-2 minutes until evenly mixed; S3. Fiber dispersion: Slowly add the modified basalt fiber obtained in step S1 into the mixer and continue to dry mix for 2-3 minutes to make the fiber evenly dispersed in the dry material; S4. Wet mixing and molding: Add mixing water, water-reducing agent solution and defoamer to the mixer, and wet mix for 3-5 minutes to obtain concrete mixture; wherein the water-cement ratio is 0.35-0.45; S5. Pouring and curing: Pour the mixture into the mold, vibrate to compact it, cover to keep it moist, let it stand for 12-24 hours, then remove it from the mold and carry out standard curing.

6. The preparation method according to claim 5, characterized in that, The concrete mixture described in step S4 has a slump of 120~160mm, an expansion of ≥500mm, and no visible fiber clumping or bleeding.

7. The preparation method according to claim 5, characterized in that, In steps S2 to S4, a twin-shaft forced mixer is used for mixing.

8. The preparation method according to claim 5, characterized in that, In step S5, an immersion vibrator is used for compaction at a frequency of 12,000 times per minute. The compaction time at each compaction point is 20 to 30 seconds until the concrete surface is covered with slurry and no air bubbles overflow.

9. The preparation method according to claim 5, characterized in that, The modified basalt fiber in step S3 is added at a rate of 0.1% to 1.2% of the concrete volume, and the fiber should be added in a concentrated manner.

10. The application of a water-reducing agent in the surface modification of basalt fibers, characterized in that, The water-reducing agent is a copolymer containing carboxyl, amino and polyether side chains prepared according to step (1) of claim 1.

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