A sulfate-attacking resistant concrete and a method for preparing the same

Abstract

The present application relates to the technical field of concrete preparation, and particularly relates to a sulfate-erosion-resistant concrete and a preparation method thereof, which comprises the following components in parts by weight: cement 230-310 parts, fly ash 75-87 parts, coarse aggregate 515-620 parts, fine aggregate 376-408 parts, water reducing agent 3-5 parts, modified basalt fiber 2-3 parts, functional additive 1-2 parts, and water 143-162 parts. The present application optimizes the concrete formula system, introduces modified basalt fiber and functional additive, and constructs a multiple protection system combining physical barrier and chemical protection, thereby effectively improving the sulfate-erosion-resistant performance of the concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete preparation technology, and in particular to a sulfate-resistant concrete and its preparation method. Background Technology

[0002] Sulfate attack is one of the main durability problems leading to the deterioration of concrete structures. The deterioration of concrete in a sulfate environment is a gradual process from the surface inwards: cracks develop from the surface, gradually lengthening and widening, then interconnecting to form a network of cracks. Further erosion leads to the gradual shedding of the surface layer, exposing the internal aggregate, and this cycle continues until the concrete disintegrates. The development of these cracks provides a channel for the corrosive solution to enter the concrete, further accelerating the erosion process and increasing the rate of deterioration. The main products of sulfate attack are ettringite and gypsum, both of which are insoluble, expansive crystals. When these products develop excessively within the pores and undergo physical crystallization, the resulting expansion stress, if exceeding the concrete's restraint capacity, will cause the concrete to crack, and in severe cases, disintegrate.

[0003] Chinese patent CN112266213A discloses a high-strength sulfate-resistant concrete and its preparation method. This patent uses modified basalt fiber as a reinforcing material. By grafting carboxyl groups onto the surface of the basalt fiber, the electrostatic repulsion between the ionized carboxyl groups and sulfate ions prevents sulfate from penetrating the concrete. Specifically, the patent first deposits nano-zinc oxide on the surface of the basalt fiber to increase surface roughness. Then, it utilizes the self-oxidative polymerization of dopamine to form a polydopamine layer on the fiber surface. Finally, carboxyl groups are introduced onto the fiber surface through the reaction of amino groups on the polydopamine layer with trimesoyl chloride. The patent also uses a composite of silica powder and modified basalt fiber to fill the pores of the concrete to improve density. However, the electrostatic repulsion mechanism used in this technical solution mainly serves as a barrier and is insufficient to effectively capture and solidify sulfate ions that have already entered the concrete. Furthermore, the carboxyl functional layer on the fiber surface is at risk of failure under long-term corrosive conditions, and the durability of its sulfate resistance needs further improvement. Summary of the Invention

[0004] In view of this, the present invention proposes a sulfate-resistant concrete and its preparation method to solve the problems in the prior art.

[0005] The technical solution of the present invention is implemented as follows: The present invention provides a sulfate-resistant concrete, which, by weight, comprises the following components: 230-310 parts of cement, 75-87 parts of fly ash, 515-620 parts of coarse aggregate, 376-408 parts of fine aggregate, 3-5 parts of water-reducing agent, 2-3 parts of modified basalt fiber, 1-2 parts of functional additives, 1 part of dispersant, and 143-162 parts of water.

[0006] This invention achieves multiple layers of protection against sulfate attack by optimizing the concrete formulation and introducing functional modified materials. Specifically, the composite cementitious material system composed of cement and fly ash provides the concrete with basic mechanical properties and durability. The pozzolanic activity of fly ash consumes calcium hydroxide in the hydration products, reducing the raw material source for sulfate attack reactions, while simultaneously refining the pore structure to reduce the penetration rate of eroding ions. Modified basalt fibers form a three-dimensional reinforcing network in the concrete matrix, not only inhibiting crack initiation and propagation through physical bridging and blocking the penetration channels of eroding solutions, but also capturing eroding ions on the fiber surface through a functionalized modified layer, reducing the generation of expansive erosion products at the source and preventing the penetration of eroding ionic solutions into the concrete interior. Functional additives, through the synergistic effect of chemical curing and physical filling, provide continuous protective efficacy in the concrete pore fluid and matrix, further enhancing the concrete's density and erosion resistance. The rational proportioning and synergistic effect of the above components enable the concrete to exhibit excellent crack resistance, low permeability, and long-term durability in a sulfate environment.

[0007] Based on the above technical solutions, preferably, the preparation method of the modified basalt fiber includes: S1. After pretreatment, basalt fibers are dispersed in deionized water. Then, a mixed solution of magnesium salt, aluminum salt and barium salt is added to the solution, and an alkaline solution is added dropwise to adjust the pH value. The mixture is stirred and reacted at 40-80℃ for 2-8 hours to obtain fibers loaded with hydrotalcite. S2. After washing and drying the fiber loaded with hydrotalcite, disperse it in an ethanol solution, then add an aminosilane coupling agent to it, and stir the reaction at 50-70℃ for 1-4 hours to obtain surface-modified fiber. S3. After washing and drying the surface-modified fibers, disperse them in an organic solvent, then add hydrogenated dimer acid and a catalyst, and stir the reaction at 80-120℃ for 3-8 hours to obtain modified basalt fibers.

[0008] Specifically, in step S1, magnesium, aluminum, and barium salts undergo a co-precipitation reaction under alkaline conditions to form barium-doped magnesium-aluminum layered bimetallic hydroxides (Ba-Mg-Al LDHs) in situ on the surface of basalt fibers. This layered structure possesses anion exchange capacity and pH-responsive characteristics, selectively capturing corrosive anions such as sulfate and chloride ions. Simultaneously, the roughened fiber surface enhances the mechanical bonding with the cement matrix. In step S2, an aminosilane coupling agent is used to construct a chemical bonding bridge between the LDHs layer and the fiber, significantly improving the load stability and interfacial bond strength of the LDHs layer, while introducing amino groups as active reaction sites. In step S3, the carboxyl groups of the hydrogenated dimer acid undergo an amidation reaction with the amino groups under the action of a catalyst, forming a hydrophobic modified layer with a long-chain alkyl structure on the fiber surface. This hydrophobic layer effectively prevents corrosive ionic solutions from penetrating into the concrete interior through the fiber-matrix interface transition zone, which is typically a weak point and preferential erosion channel in the concrete structure. The hydrophobically modified fiber surface forms a water barrier layer, which significantly reduces the rate of sulfate ion transport across the interface and slows down the erosion process.

[0009] Based on the above technical solutions, preferably, in step S1, the pretreatment is to treat the basalt fiber with an alkaline solution or an acid solution; the mass ratio of the basalt fiber, magnesium salt, aluminum salt and barium salt is 100 : (6-8) : (2-4) : (0.4-1).

[0010] Based on the above technical solutions, preferably, in step S1, the magnesium salt is magnesium nitrate or magnesium chloride, the aluminum salt is aluminum nitrate or aluminum chloride, and the barium salt is barium nitrate, barium chloride, or barium acetate.

[0011] Based on the above technical solutions, preferably, in step S2, the aminosilane coupling agent is KH550 or KH792; the amount of aminosilane coupling agent added is 3-8% of the mass of the loaded hydrotalcite fiber.

[0012] Based on the above technical solutions, preferably, in step S3, the mass ratio of the hydrogenated dimer acid, the catalyst, and the surface-modified fiber is (1-2):(0.05-0.2):10, and the catalyst is 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) or dicyclohexylcarbodiimide (DCC).

[0013] Based on the above technical solutions, preferably, the functional additives include sodium molybdate, metakaolin, and calcium carbonate whiskers.

[0014] Based on the above technical solutions, preferably, by weight, the functional additives contain 30-50 parts sodium molybdate, 30-45 parts metakaolin, and 20-30 parts calcium carbonate whiskers.

[0015] Specifically, molybdate ions in sodium molybdate can undergo a redox reaction on the surface of reinforcing steel to form a dense ferric molybdate passivation film. This passivation film can block oxygen and moisture from contacting the reinforcing steel, and molybdate ions have a competitive ability to occupy adsorption sites on the steel surface, significantly reducing the risk of pitting corrosion caused by chloride ions and providing continuous chemical protection. Metakaolin, as a highly active pozzolanic material, can consume calcium hydroxide in cement hydration products through its secondary hydration reaction, reducing the calcium source supply for sulfate corrosion. At the same time, the generated hydrated calcium silicate gel refines and fills the pore structure, reducing the permeability coefficient of the corrosive solution. Calcium carbonate whiskers, as nano- and micro-scale fibrous reinforcing materials, have a high aspect ratio that allows them to bridge cracks at the microscale of the cement matrix, compensating for microcrack areas that are difficult for macroscopic basalt fibers to reach, forming a multi-scale crack-resistant network from nanoscale to macroscale. The synergistic effect of functional additives and modified basalt fibers achieves a chemical-physical enhancement of concrete's resistance to erosion: sodium molybdate provides planar chemical protection throughout the pore fluid, while the modified fibers provide point-like physical-chemical dual protection in cracks and weak areas; the rapid film-forming response of sodium molybdate and the long-term ion trapping effect of LDHs on the modified fiber surface form a velocity gradient protection; the scale complementarity between calcium carbonate whiskers and basalt fibers achieves full coverage inhibition of cracks of different widths. This multi-dimensional synergistic effect enables concrete to exhibit excellent impermeability, crack resistance, and steel reinforcement protection in sulfate-eroded environments.

[0016] Based on the above technical solutions, preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0017] This invention also provides a method for preparing sulfate-resistant concrete, the method comprising: Cement, fly ash, functional additives, coarse aggregate, and fine aggregate are put into a mixer and dry-mixed for 1-3 minutes to obtain a dry mix. The water-reducing agent is mixed evenly with water and then added to the dry mix. The mixture is stirred for 3-5 minutes to obtain a premix. Modified basalt fiber is added evenly in batches to the premix and stirred for 2-4 minutes to obtain a premix. The premix is ​​then cured to obtain sulfate-resistant concrete.

[0018] The sulfate-resistant concrete and its preparation method of the present invention have the following advantages over the prior art: (1) This invention optimizes the concrete formulation system, introduces modified basalt fibers and functional additives, and constructs a multi-layer protection system that combines physical barriers and chemical protection, effectively improving the concrete's resistance to sulfate attack. The three-dimensional reinforcing network formed by the modified fibers in the matrix inhibits the initiation and propagation of cracks and blocks the penetration channels of the corrosive solution; the functional additives reduce the amount of expansive corrosion products and expansive stress from multiple levels by consuming the calcium source of the corrosion reaction, refining the pore structure and capturing corrosive ions; the synergistic effect of the two makes the concrete exhibit a lower mass loss rate, a higher compressive strength retention rate and better apparent integrity in the sulfate environment, thus improving the durability of the concrete against sulfate attack.

[0019] (2) This invention achieves a comprehensive improvement in fiber performance by modifying basalt fibers. By adding barium-doped magnesium aluminum hydrotalcite to the fibers, the fibers are endowed with anion exchange capacity, enabling them to actively capture and fix corrosive anions such as sulfate and chloride ions, thus delaying the corrosion process. The grafting of silane coupling agent establishes a stable chemical bond between the LDHs layer and the fiber, preventing the functional layer from falling off and failing in alkaline pore liquid, and ensuring the long-term effectiveness of the ion capture function. The hydrophobicity introduced by the surface modification of hydrogen dimer acid mainly undertakes the functions of water barrier and stress buffer. The three-layer structure forms a gradient interface structure of "chemical bonding-mechanical interlocking-hydrophobic protection". Through the above technical solutions, the modified fibers have both chemical protection and physical reinforcement functions.

[0020] (3) The functional additive compound system adopted in this invention achieves an organic combination of chemical inhibition and physical enhancement. Sodium molybdate provides continuous chemical protection in the pore fluid. Molybdate ions form a passivation film on the surface of the steel reinforcement and competitively occupy adsorption sites, reducing the risk of chloride ion-induced steel reinforcement corrosion. Metakaolin consumes calcium hydroxide and refines the pore structure through secondary hydration reaction, reducing the raw material supply for sulfate corrosion reaction from the source and reducing the penetration rate of the corrosive medium. Calcium carbonate whiskers bridge microcracks at the microscale and form a multi-scale crack-resistant network with macroscopic basalt fibers. The synergistic effect of the three components enables the functional additives to exert a significant synergistic effect at a low dosage. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1This is a diagram showing the pore structure distribution characteristics of a concrete specimen after 28 days of curing, according to Example 1 of the present invention. Figure 2 The surface damage morphology of concrete specimens used in embodiments and comparative examples of the present invention after 180 cycles of wet-dry sulfate erosion. Figure 3 Electron micrographs of concrete specimens from embodiments and comparative examples of the present invention after 180 cycles of wet-dry sulfate etching. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that the cement used is China Red Lion brand ordinary Portland cement PO.42.5, the fly ash is grade A fly ash from Chengdu Donglanxing New Materials Co., Ltd. in Sichuan, and the coarse aggregate is crushed stone with an apparent density of 2645 kg / m³. 3 The fine aggregate is manufactured sand with a fineness modulus of 2.7, and the water-reducing agent is polycarboxylate water-reducing agent from Shanxi Chengxin Poly Company.

[0025] Example 1

[0026] This embodiment discloses a sulfate-resistant concrete and its preparation method. By weight, it comprises the following components: 270 parts cement, 81 parts fly ash, 568 parts coarse aggregate, 392 parts fine aggregate, 4 parts water-reducing agent, 2.5 parts modified basalt fiber, 1.5 parts functional additives, and 153 parts water. The functional additives include: 40 parts sodium molybdate, 37 parts metakaolin, and 25 parts calcium carbonate whiskers. The preparation method is as follows: (1) Preparation of modified basalt fibers: S1. Basalt fibers were soaked in a 5% sodium hydroxide solution at 60°C for 30 minutes, then washed with deionized water until neutral, and dried at 80°C for 2 hours to obtain pretreated fibers. 100g of the pretreated fibers were dispersed in 1000ml of deionized water, and 7g of magnesium nitrate, 3g of aluminum nitrate, and 0.7g of barium nitrate were dispersed in 500ml of deionized water to form a mixed salt solution. The mixed salt solution was slowly added to the fiber suspension under mechanical stirring, while adjusting the pH to 9-10 with 1mol / L sodium hydroxide solution and controlling the dropping rate to keep the pH stable. The system was heated to 60°C and stirred for 5 hours. After the reaction was completed, the product was filtered and separated, washed, and dried to obtain fibers loaded with hydrotalcite. S2. 100g of fiber loaded with hydrotalcite was dispersed in 800mL of 95% ethanol solution and ultrasonically dispersed for 10min. Then, 6g of KH550 was added and the mixture was stirred at 60℃ for 2.5h. After the reaction was completed, the product was filtered and separated, washed and dried to obtain surface-modified fiber. S3. Disperse 100g of surface-modified fiber in 1000mL of dimethylformamide (DMF) and sonicate for 10min. Then add 15g of hydrogenated dimer acid and 1.2g of EDC and stir at 100℃ for 5h. After the reaction is complete, filter the product, wash and dry it to obtain modified basalt fiber.

[0027] (2) Preparation of functional additives: 40 parts of sodium molybdate, 37.5 parts of metakaolin and 25 parts of calcium carbonate whiskers were put into a high-speed mixer and mixed at 500 rpm for 15 min to obtain functional additives. After passing through a 100-mesh sieve, the additives were stored for later use.

[0028] (3) Add cement, fly ash, functional additives, coarse aggregate and fine aggregate into a mixer in proportion, dry mix at 60 rpm for 2 minutes to ensure uniform mixing of each component, and obtain dry mix; after uniformly mixing water-reducing agent with water, add it to the dry mix and stir for 4 minutes to obtain a mixture; add modified basalt fiber evenly to the mixture in 3 batches and stir for 3 minutes to obtain a premix; pour the premix into a pre-prepared standard mold, vibrate on a vibrating table for 10-15 seconds to remove air bubbles, and smooth the surface. Immediately after the specimen is formed, cover it with plastic film to prevent moisture evaporation, let it stand at room temperature (20±2℃) for 24 hours, then demold it, and then place the specimen in a standard curing room (temperature 20±2℃, relative humidity ≥95%) to cure for the specified age (28 days) to obtain sulfate-resistant concrete.

[0029] Example 2

[0030] This embodiment discloses a sulfate-resistant concrete and its preparation method. By weight, it comprises the following components: 230 parts cement, 75 parts fly ash, 515 parts coarse aggregate, 376 parts fine aggregate, 3 parts water-reducing agent, 2 parts modified basalt fiber, 1 part functional additive, and 143 parts water. The functional additive includes: 30 parts sodium molybdate, 30 parts metakaolin, and 20 parts calcium carbonate whiskers. The preparation method is as follows: (1) Preparation of modified basalt fibers: S1. Basalt fibers were soaked in a 5% sodium hydroxide solution at 60°C for 30 minutes, then washed with deionized water until neutral, and dried at 80°C for 2 hours to obtain pretreated fibers. 100g of the pretreated fibers were dispersed in 1000ml of deionized water, and 6g of magnesium nitrate, 2g of aluminum nitrate, and 0.4g of barium nitrate were dispersed in 500ml of deionized water to form a mixed salt solution. The mixed salt solution was slowly added to the fiber suspension under mechanical stirring, while adjusting the pH to 9-10 with 1mol / L sodium hydroxide solution and controlling the dropping rate to keep the pH stable. The system was heated to 40°C and stirred for 8 hours. After the reaction was completed, the product was filtered and separated, washed, and dried to obtain fibers loaded with hydrotalcite. S2. 100g of fiber loaded with hydrotalcite was dispersed in 800mL of 95% ethanol solution and ultrasonically dispersed for 10min. Then, 3g of KH550 was added and stirred at 50℃ for 4h. After the reaction was completed, the product was filtered and separated, washed and dried to obtain surface-modified fiber. S3. Disperse 100g of surface-modified fiber in 1000mL of dimethylformamide (DMF) and sonicate for 10min. Then add 10g of hydrogenated dimer acid and 0.5g of EDC and stir at 80℃ for 8h. After the reaction is complete, filter the product, wash and dry it to obtain modified basalt fiber.

[0031] (2) Preparation of functional additives: 30 parts of sodium molybdate, 30 parts of metakaolin and 20 parts of calcium carbonate whiskers were put into a high-speed mixer and mixed at 500 rpm for 15 min to obtain functional additives. After passing through a 100-mesh sieve, the additives were stored for later use.

[0032] (3) Add cement, fly ash, functional additives, coarse aggregate and fine aggregate into a mixer in proportion, dry mix at 60 rpm for 1 min to ensure uniform mixing of each component, and obtain dry mix; after uniformly mixing water-reducing agent with water, add it to the dry mix and stir for 3 min to obtain a mixture; add modified basalt fiber evenly to the mixture in 3 batches and stir for 2 min to obtain a premix; pour the premix into a pre-prepared standard mold, vibrate on a vibrating table for 10-15 s to remove air bubbles, and smooth the surface. Immediately after the specimen is formed, cover it with plastic film to prevent moisture evaporation, let it stand at room temperature (20±2℃) for 24 h, then demold it, and then place the specimen in a standard curing room (temperature 20±2℃, relative humidity ≥95%) to cure for the specified age (28d) to obtain sulfate-resistant concrete.

[0033] Example 3

[0034] This embodiment discloses a sulfate-resistant concrete and its preparation method. By weight, it comprises the following components: 310 parts cement, 87 parts fly ash, 620 parts coarse aggregate, 408 parts fine aggregate, 5 parts water-reducing agent, 3 parts modified basalt fiber, 2 parts functional additives, and 162 parts water. The functional additives include: 50 parts sodium molybdate, 45 parts metakaolin, and 30 parts calcium carbonate whiskers. The preparation method is as follows: (1) Preparation of modified basalt fibers: S1. Basalt fibers were soaked in a 5% sodium hydroxide solution at 60°C for 30 minutes, then washed with deionized water until neutral, and dried at 80°C for 2 hours to obtain pretreated fibers. 100g of the pretreated fibers were dispersed in 1000ml of deionized water, and 8g of magnesium nitrate, 4g of aluminum nitrate, and 1g of barium nitrate were dispersed in 500ml of deionized water to form a mixed salt solution. The mixed salt solution was slowly added to the fiber suspension under mechanical stirring, while adjusting the pH to 9-10 with 1mol / L sodium hydroxide solution and controlling the dropping rate to keep the pH stable. The system was heated to 80°C and stirred for 2 hours. After the reaction was completed, the product was filtered and separated, washed, and dried to obtain fibers loaded with hydrotalcite. S2. 100g of fiber loaded with hydrotalcite was dispersed in 800mL of 95% ethanol solution and ultrasonically dispersed for 10min. Then, 8g of KH550 was added and stirred at 70℃ for 1h. After the reaction was completed, the product was filtered and separated, washed and dried to obtain surface-modified fiber. S3. Disperse 100g of surface-modified fiber in 1000mL of dimethylformamide (DMF) and sonicate for 10min. Then add 20g of hydrogenated dimer acid and 2g of EDC and stir at 120℃ for 3h. After the reaction is complete, filter the product, wash and dry it to obtain modified basalt fiber.

[0035] (2) Preparation of functional additives: 50 parts of sodium molybdate, 45 parts of metakaolin and 30 parts of calcium carbonate whiskers were put into a high-speed mixer and mixed at 500 rpm for 15 min to obtain functional additives. After passing through a 100-mesh sieve, the additives were stored for later use.

[0036] (3) Add cement, fly ash, functional additives, coarse aggregate and fine aggregate into a mixer in proportion, dry mix at 60 rpm for 3 minutes to ensure uniform mixing of each component, and obtain dry mix; after uniformly mixing water-reducing agent with water, add it to the dry mix and stir for 5 minutes to obtain a mixture; add modified basalt fiber evenly to the mixture in 3 batches and stir for 4 minutes to obtain a premix; pour the premix into a pre-prepared standard mold, vibrate on a vibrating table for 10-15 seconds to remove air bubbles, and smooth the surface. Immediately after the specimen is formed, cover it with plastic film to prevent moisture evaporation, let it stand at room temperature (20±2℃) for 24 hours, then demold it, and then place the specimen in a standard curing room (temperature 20±2℃, relative humidity ≥95%) to cure for the specified age (28 days) to obtain sulfate-resistant concrete.

[0037] Comparative Example 1 This comparative example discloses a sulfate-resistant concrete and its preparation method. Its components and preparation method are the same as in Example 1, except that: (2) Preparation of functional additives: 77 parts of metakaolin and 25 parts of calcium carbonate whiskers were put into a high-speed mixer and mixed at 500 rpm for 15 min to obtain functional additives. After passing through a 100-mesh sieve, the additives were stored for later use.

[0038] Comparative Example 2 This comparative example discloses a sulfate-resistant concrete and its preparation method. Its components and preparation method are the same as in Example 1, except that: modified basalt fibers are loaded with magnesium aluminum hydrotalcite, specifically including: S1. Basalt fibers were soaked in a 5% sodium hydroxide solution at 60°C for 30 minutes, then washed with deionized water until neutral, and dried at 80°C for 2 hours to obtain pretreated fibers. 100g of the pretreated fibers were dispersed in 1000ml of deionized water, and 7.7g of magnesium nitrate and 3g of aluminum nitrate were dispersed in 500ml of deionized water to form a mixed salt solution. The mixed salt solution was slowly added to the fiber suspension under mechanical stirring, while adjusting the pH to 9-10 with 1mol / L sodium hydroxide solution and controlling the dropping rate to keep the pH stable. The system was heated to 60°C and stirred for 5 hours. After the reaction was completed, the product was filtered and separated, washed, and dried to obtain fibers loaded with hydrotalcite. The remaining steps are the same as in Example 1.

[0039] Comparative Example 3 This comparative example discloses a sulfate-resistant concrete and its preparation method. Its components and preparation method are the same as in Example 1, except that the modified basalt fibers are not grafted with hydrogenated dimer acid, specifically including: S1. Basalt fibers were soaked in a 5% sodium hydroxide solution at 60°C for 30 minutes, then washed with deionized water until neutral, and dried at 80°C for 2 hours to obtain pretreated fibers. 100g of the pretreated fibers were dispersed in 1000ml of deionized water, and 7g of magnesium nitrate, 3g of aluminum nitrate, and 0.7g of barium nitrate were dispersed in 500ml of deionized water to form a mixed salt solution. The mixed salt solution was slowly added to the fiber suspension under mechanical stirring, while adjusting the pH to 9-10 with 1mol / L sodium hydroxide solution and controlling the dropping rate to keep the pH stable. The system was heated to 60°C and stirred for 5 hours. After the reaction was completed, the product was filtered and separated, washed, and dried to obtain fibers loaded with hydrotalcite. S2. 100g of fiber loaded with hydrotalcite was dispersed in 800mL of 95% ethanol solution and ultrasonically dispersed for 10min. Then, 6g of KH550 was added and the mixture was stirred at 60℃ for 2.5h. After the reaction was completed, the product was filtered and separated, washed and dried to obtain modified basalt fiber.

[0040] Comparative Example 4 This comparative example discloses a sulfate-resistant concrete and its preparation method. Its components and preparation method are the same as in Example 1, except that the modified basalt fibers are not chemically grafted with hydrogenated dimer acid. Specifically, it includes: S1. Basalt fibers were soaked in a 5% sodium hydroxide solution at 60°C for 30 minutes, then washed with deionized water until neutral, and dried at 80°C for 2 hours to obtain pretreated fibers. 100g of the pretreated fibers were dispersed in 1000ml of deionized water, and 7g of magnesium nitrate, 3g of aluminum nitrate, and 0.7g of barium nitrate were dispersed in 500ml of deionized water to form a mixed salt solution. The mixed salt solution was slowly added to the fiber suspension under mechanical stirring, while adjusting the pH to 9-10 with 1mol / L sodium hydroxide solution and controlling the dropping rate to keep the pH stable. The system was heated to 60°C and stirred for 5 hours. After the reaction was completed, the product was filtered and separated, washed, and dried to obtain fibers loaded with hydrotalcite. S2. Disperse 100g of hydrotalcite-loaded fibers in 1000mL of anhydrous ethanol and sonicate for 10min. Add 15g of hydrogenated dimer acid and stir at room temperature (25℃) for 2h at a stirring speed of 200rpm to allow the hydrogenated dimer acid to adhere to the fiber surface through physical adsorption. After blending, filter the product, wash and dry to obtain modified basalt fibers.

[0041] Performance testing 1. SEM scanning: The microstructure of the concrete after corrosion damage was observed using SEM and energy dispersive spectroscopy. Sections were prepared, and fragments were obtained from 0-15 mm and 45-60 mm.

[0042] 2. By testing the pore size, average chord length of pore bubbles, and bubble spacing of concrete after 28 days of curing and hardening, the distribution of pores inside the hardened concrete was analyzed.

[0043] 3. Compressive Strength and Erosion Resistance Coefficient: According to GB / T 50081-2019, a 300T microcomputer-controlled electro-hydraulic servo pressure testing machine was used to conduct compressive strength tests on concrete specimens. The tests were conducted under stress control with a loading rate of 0.5 MPa / s. The selected loading rate for compressive strength was 0.6 MPa / s. The arithmetic mean of the compressive strength of three parallel cubic specimens was used as the test result to ensure the accuracy and reliability of the compressive strength under different conditions. According to the relevant provisions of national standard GB / T50082-2024 regarding sulfate resistance and chloride ion penetration tests: Where: Kf -- compressive strength corrosion resistance coefficient (%); fcn -- is the measured compressive strength (MPa) of a concrete specimen subjected to sulfate corrosion and chloride ion penetration after N wet-dry cycles, accurate to 0.1 MPa; fc0 -- The measured compressive strength (MPa) of a standard-cured concrete specimen at the same age as specimens subjected to sulfate corrosion and chloride ion penetration, accurate to 0.1 MPa.

[0044] 4. Mass Change: The mass change pattern of eroded concrete can intuitively reflect the process of erosion products filling and cracking / stripping. After the specimens reached the planned erosion age, they were removed, the surface moisture was wiped off, and they were ventilated at room temperature for 3 hours before being weighed. The electronic scale used in this experiment had a testing accuracy of 0.1g. The mass of each group of specimens was measured every 15 days in a wet-dry cycle. The average mass of the three groups of specimens was taken as the representative value of the data result. The three specimens selected under different erosion conditions were kept consistent to ensure the comparability of the test results. The mass change rate ΔW of the specimen was calculated using the following formula: In the formula: △W is the mass loss rate of the concrete specimen after the nth wet-dry cycle, in % %. W0 represents the initial mass of the concrete specimen after 28 days of curing, in grams. Wn represents the mass of the concrete specimen after the nth wet-dry cycle, in grams.

[0045] Table 1 Performance Test Results Figure 1 The figure shows the pore structure distribution characteristics of the concrete in Example 1 after 28 days of curing. As can be seen from the figure, the pore diameter is mainly concentrated in the range of 0-100 μm, dominated by capillary pores and gel pores smaller than 50 μm, with the diameter percentage peak occurring in the 0-20 μm range. The content of macropores (>100 μm) is extremely low, and the pore content percentage curve remains at a low level overall. The embedded local SEM test image shows that the internal structure of the concrete is dense, with dispersed and small-sized pores (marked in green). This optimized pore structure, dominated by fine pores and low in macropores, effectively reduces the penetration channels of corrosive ions, thus exhibiting good resistance to sulfate attack.

[0046] Figure 2 The surface damage morphology of concrete specimens with different formulations after 180 cycles of wet and dry sulfate erosion is shown. Among them: Figure (a) is the concrete specimen of Example 1, the surface remains intact and dense, with only slight cracks in local areas (marked by red circles), and very little erosion products are attached, demonstrating the excellent anti-erosion performance under the synergistic effect of modified fibers and functional additives; Figure (b) is the concrete specimen of Comparative Example 1, which is the specimen of Comparative Example 1. Because no sodium molybdate passivating agent was added to the functional additives, a small number of cracks and slight erosion products appeared on the surface; Figure (c) is the concrete specimen of Comparative Example 2. The lack of barium doping on the fiber surface resulted in insufficient ion capture ability, and a large number of white expansive erosion products were deposited and network cracks appeared on the surface; Figure (d) is the concrete specimen of Comparative Example 3. Because the fiber surface completely lacks the hydrophobic modification layer, the dispersion is poor and the stress concentration in the interface transition zone is high, it exhibits the most severe network cracks and surface fragmentation, and the erosion damage is the most severe; Figure (e) is the concrete specimen of Comparative Example 4. The fiber only physically adsorbs the hydrophobic layer rather than chemically bonding, which leads to weakened fiber-matrix interface bonding, and obvious cracking and local peeling phenomena appear on the surface.

[0047] Figure 3The microstructure and morphology of corrosion products in concrete specimens with different formulations after 180 cycles of wet and dry sulfate corrosion are shown. Specifically: Figure (a) shows the concrete specimen of Example 1, where the CSH gel matrix structure is relatively dense and intact. Although a small amount of gypsum and ettringite (AFt) corrosion products are observed, their quantity is significantly less than in other samples. The ion-trapping function of the three-step chemically modified fibers and the synergistic protection of the functional additives effectively inhibited the generation and accumulation of corrosion products. Figure (b) shows the concrete specimen of Comparative Example 1, where the CSH matrix is ​​relatively intact, and the number of AFt needle-like crystals is limited. However, due to the lack of chemical protection from sodium molybdate passivator, corrosion product enrichment begins to appear in localized areas. Figure (c) shows the concrete specimen of Comparative Example 2, where obvious cracks are visible, indicating gypsum and AFt corrosion. The products increased significantly. The lack of a barium-doped magnesium aluminum hydrotalcite layer on the fiber surface resulted in insufficient sulfate ion capture capacity, and a large amount of expansive erosion products were generated in the matrix. Figure (d) shows the concrete specimen of Comparative Example 3. A large number of dense AFt needle-like crystals filled the CSH matrix, and the erosion products were the most numerous and densely distributed. The uneven dispersion and interfacial stress concentration caused by the complete absence of the hydrophobic modification layer on the fiber surface led to the most severe microstructure deterioration. Figure (e) shows the concrete specimen of Comparative Example 4. The cracks were obvious, and there were more gypsum and AFt erosion products. The fiber only physically adsorbed the hydrophobic layer rather than chemically bonded, which made the fiber-matrix interface transition zone a preferential entry channel for erosion ions.

[0048] According to the data in Table 1, the compressive strength of Examples 1-3 was 53.8-58.3 MPa, and the erosion coefficient remained at 92.4%-94.5% after 180 wet-dry cycles, with a mass loss rate of only 0.32%-0.45%. In contrast, the compressive strength of Comparative Examples 1-4 decreased to 47.5-51.2 MPa, and the erosion coefficient decreased to 77.6%-81.5% after 180 cycles, with a mass loss rate as high as 1.38%-2.14%. Comparative Example 3 had the worst performance, indicating that the hydrophobic modification layer is crucial for improving the fiber-matrix interface bonding strength and blocking the penetration of corrosive media. Comparative Example 2 was the second best, verifying the key role of barium doping in enhancing the ion trapping ability of the hydrotalcite layer. Although Comparative Example 4 was better than Comparative Example 3, it was still significantly worse than the examples, proving the necessity of chemical bonding with silane coupling agents. The long-term mass loss rate of Comparative Example 1 was significantly higher than that of the examples, reflecting the role of sodium molybdate in passivating steel bars and slowing down corrosion. In summary, this invention employs a three-step chemical grafting strategy—in-situ growth of barium-doped hydrotalcite on the surface of modified basalt fibers, silane coupling agent bridging, and hydrophobic modification with hydrogenated dimer acid—combined with the synergistic effect of functional additives, to construct a multi-layered protection system that integrates physical barriers and chemical protection. This significantly improves the compressive strength, sulfate resistance, and long-term durability of concrete.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sulphate attack resistant concrete, characterized in that: The product comprises, by weight, the following components: 230-310 parts cement, 75-87 parts fly ash, 515-620 parts coarse aggregate, 376-408 parts fine aggregate, 3-5 parts water-reducing agent, 2-3 parts modified basalt fiber, 1-2 parts functional additives, and 143-162 parts water; the functional additives, by weight, comprise the following components: 30-50 parts sodium molybdate, 30-45 parts metakaolin, and 20-30 parts calcium carbonate whiskers. The preparation method of the modified basalt fiber includes: S1. After pretreatment, basalt fibers are dispersed in deionized water. Then, a mixed solution of magnesium salt, aluminum salt and barium salt is added to the solution, and an alkaline solution is added dropwise to adjust the pH value. The reaction is stirred at 40℃-80℃ for 2-8 hours to obtain fibers loaded with hydrotalcite. S2. After washing and drying the fiber loaded with hydrotalcite, disperse it in an ethanol solution, then add an aminosilane coupling agent to it, and stir the reaction at 50℃-70℃ for 1-4 hours to obtain surface-modified fiber. S3. After washing and drying the surface-modified fibers, disperse them in an organic solvent, then add hydrogenated dimer acid and a catalyst, and stir the reaction at 80℃-120℃ for 3-8 hours to obtain modified basalt fibers.

2. A sulphate attack resistant concrete as claimed in claim 1, wherein: In step S1, the pretreatment involves treating the basalt fiber with an alkaline solution or an acid solution; the mass ratio of the basalt fiber, magnesium salt, aluminum salt, and barium salt is 100 : 6-8 : 2-4 : 0.4-1.

3. The sulfate attack resistant concrete of claim 1, wherein: In step S1, the magnesium salt is magnesium nitrate or magnesium chloride, the aluminum salt is aluminum nitrate or aluminum chloride, and the barium salt is one of barium nitrate, barium chloride, and barium acetate.

4. The sulfate attack resistant concrete of claim 1, wherein: In step S2, the aminosilane coupling agent is KH550 or KH792; the amount of aminosilane coupling agent added is 3%-8% of the mass of the loaded hydrotalcite fiber.

5. The sulfate attack resistant concrete of claim 1, wherein: In step S3, the mass ratio of the hydrogenated dimer acid, the catalyst, and the surface-modified fiber is 1-2:0.05-0.2:10, and the catalyst is 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride or dicyclohexylcarbodiimide.

6. The sulfate attack resistant concrete of claim 1, wherein: The water-reducing agent is a polycarboxylate water-reducing agent.

7. A method of producing a sulphate attack resistant concrete according to any one of claims 1 to 6, characterised in that: The preparation method includes: Cement, fly ash, functional additives, coarse aggregate, and fine aggregate are put into a mixer and dry-mixed for 1-3 minutes to obtain a dry mix. The water-reducing agent is mixed evenly with water and then added to the dry mix. The mixture is stirred for 3-5 minutes to obtain a premix. Modified basalt fiber is added evenly in batches to the premix and stirred for 2-4 minutes to obtain a premix. The premix is ​​then cured to obtain sulfate-resistant concrete.

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