Basalt fiber sea sand concrete and preparation method and application thereof

Abstract

This invention discloses a basalt fiber-reinforced seawater sand concrete, its preparation method, and its application, belonging to the field of building materials technology. The basalt fiber-reinforced seawater sand concrete, by weight, consists of the following components: 35-45 parts cement, 65-75 parts sea sand, 105-120 parts crushed stone, 15-20 parts seawater, 0.1-0.3 parts water-reducing agent, and 0.1-1 parts basalt fiber. Based on the selection of raw materials and mix design to improve the toughness and crack resistance of traditional concrete, SEM results show that the addition of basalt fiber to seawater sand concrete bridges cracks and improves pore connectivity, which is beneficial for improving crack resistance, toughness, salt and alkali resistance, and residual mechanical properties after high temperatures. It can be used for the repair of shield tunnel segments, FRP concrete structures, and existing structures in marine environments.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a basalt fiber seawater sand concrete and its preparation method and application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Seawater sea-sand concrete (SSC), as a novel marine concrete material with locally sourced raw materials, has demonstrated significant economic and construction efficiency advantages in marine engineering projects such as cross-sea bridges and breakwaters. The high salinity of seawater alters the cement hydration process, and the presence of SO4 in seawater... 2- Mg 2+ Components such as these can cause SSC to generate large amounts of expansive ettringite and gypsum, leading to internal volume expansion and increased porosity in the concrete. Mg in seawater... 2+ It can react with Ca(OH)2 in the gelling system to form Mg(OH)2, and with the amount of Ca in the system... 2+ The continuous consumption of CSH gels induces decalcification, ultimately forming magnesium silicate hydrate (MSH) with poor mechanical properties. This reaction process leads to the loosening of the cementitious structure, weakening the long-term stability and durability of SSC in highly corrosive environments, and making SSC prone to brittle fracture under bending and tensile loads. Marine engineering structures may also be subjected to high temperatures in fire or localized high-temperature scenarios. Dehydration of the cement matrix, vaporization of pore water, and mismatch between aggregate and paste thermal deformation can further induce microcrack propagation, resulting in a decrease in the residual mechanical properties of concrete after high temperatures. This makes it difficult to meet the mechanical performance, durability, and post-disaster safety requirements of marine structures such as breakwaters and cross-sea bridges.

[0004] Traditional concrete still has significant shortcomings when applied to coastal tunnel shield segments, fiber-reinforced polymer (FRP) concrete structures, and the reinforcement and repair of existing concrete structures in marine environments: its inherent brittleness and limited crack resistance and toughening properties make it difficult to adapt to the long-term complex stress conditions of shield segments, leading to early cracking; in FRP concrete structures, the interface matching and synergistic stress effect between traditional concrete and FRP materials are generally poor, making it difficult to fully utilize the overall performance of the composite material; in the high-salt, high-chloride environment of the ocean, the impermeability and erosion resistance of traditional concrete are relatively weak, and long-term service still suffers from problems such as steel corrosion and concrete deterioration, limiting structural durability and service life; when used for the reinforcement and repair of existing structures in marine environments, the compatibility of traditional concrete with the original structure is limited, and its ability to control cracks and retain residual strength after high-temperature damage is insufficient, making it difficult to improve structural durability and achieve long-term stable service. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide basalt fiber-modified seawater sand concrete, its preparation method, and its application. By modifying seawater sand concrete with short-cut basalt fibers, the invention solves the problems of poor flexural and tensile strength, and insufficient suitability for saline-alkali environments in traditional seawater sand concrete. Simultaneously, it overcomes the limitations of polypropylene fiber and glass fiber modification effects, as well as their lack of corrosion resistance. This significantly improves the flexural and tensile strength of the concrete, its suitability for saline-alkali environments, and its high-temperature resistance. Furthermore, this concrete possesses excellent workability, economy, and environmental friendliness, and can be widely applied in various coastal engineering projects, meeting their stringent performance requirements for marine concrete.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a basalt fiber seawater sand concrete, which, by weight, is composed of the following components: 35-45 parts cement, 65-75 parts sea sand, 105-120 parts crushed stone, 15-20 parts seawater, 0.1-0.3 parts water-reducing agent, and 0.1-1 parts basalt fiber. The basalt fiber is a short-cut basalt fiber with a single filament diameter of 10-20 μm, a length of 4-8 mm, a tensile strength of 1000-1200 MPa, an elastic modulus of 72-78 GPa, and a density of 2.6-2.7 g / cm³. 3 ; Short-cut basalt fibers are evenly distributed in concrete and form a fiber bridging network inside it; The method for preparing basalt fiber seawater sand concrete includes the following steps: Cement, sea sand, and crushed stone are dry-mixed to obtain dry material; water-reducing agent is dissolved in seawater to obtain mixed solution; the mixed solution and dry material are mixed and stirred, and then basalt fiber is added and stirred; after stirring, it is poured into mold, and after demolding, it is cured according to standard to the specified age.

[0007] Secondly, the present invention provides a method for preparing the above-mentioned basalt fiber seawater sand concrete, comprising the following steps: Cement, sea sand, and crushed stone are dry-mixed to obtain dry material; water-reducing agent is dissolved in seawater to obtain mixed solution; the mixed solution and dry material are mixed and stirred, and then basalt fiber is added and stirred; after stirring, it is poured into mold, and after demolding, it is cured according to standard to the specified age.

[0008] Thirdly, the present invention provides applications of the above-mentioned basalt fiber seawater sand concrete or the basalt fiber seawater sand concrete prepared by the above-mentioned preparation method. The applications include, but are not limited to: crack resistance and toughening of shield tunnel segments in coastal tunnels, or fiber reinforced polymer (FRP) concrete structures, or reinforcement, repair and durability improvement of existing concrete structures in marine environments.

[0009] One or more of the above technical solutions have the following advantages or beneficial effects: 1. This invention provides a basalt fiber-reinforced seawater sand concrete. Based on the selection of raw materials and mix design, it improves the toughness and crack resistance of traditional concrete. The addition of basalt fibers to the seawater sand concrete creates a three-dimensional network that significantly enhances the splitting tensile strength and flexural strength of the concrete. Simultaneously, the dense fiber structure hinders the penetration of chloride and sulfate ions, improving resistance to salt and alkali corrosion and extending the service life of the structure. It also boasts low-carbon and environmentally friendly advantages, effectively solving the problem of freshwater sand scarcity in marine engineering. It can be applied to toughening and crack resistance of shield tunnel segments in coastal areas, adapting to the construction of FRP-reinforced coastal engineering structures, and for the rapid repair and durability improvement of existing concrete structures in marine environments.

[0010] 2. High tensile and flexural strength. The 28-day cubic compressive strength of concrete without basalt fiber is 49.3 MPa, the 28-day splitting tensile strength is 3.6 MPa, and the 28-day flexural strength is 6.4 MPa. The basalt fiber-reinforced seawater sand concrete of this invention has a 28-day cubic compressive strength of 49.6 MPa, a 28-day splitting tensile strength of 5.0 MPa, and a 28-day flexural strength of 7.9 MPa. Compared with concrete without basalt fiber, the compressive strength is basically the same, while the splitting tensile strength is increased by 38.9% and the flexural strength by 23.4%. While ensuring compressive strength, it effectively improves the toughness and crack resistance of the concrete. SEM test results are as follows...Figure 10 As shown, short-cut basalt fibers are distributed in the concrete matrix and form a "bridging" constraint on both sides of the crack. When subjected to tension or bending, the fibers can bear part of the tensile stress and transfer the load by relying on the bond between the fiber and the slurry interface, thus delaying the propagation of microcracks and providing microscopic support for improving splitting tensile strength and flexural strength.

[0011] 3. Significantly Enhanced Early Strength. The basalt fiber seawater sand concrete of this invention utilizes the naturally occurring salt components in seawater to stimulate the hydration potential of the cementitious materials. Chloride ions and sulfates synergistically accelerate the reaction of clinker minerals, and the three-dimensional constraint network of basalt fibers rapidly builds a dense early-stage skeleton, exhibiting superior early-strength characteristics. The material reaches the set strength standard within a relatively short age, significantly accelerating the removal of on-site formwork and the hoisting of components, effectively breaking the waiting limitations of conventional construction periods. Simultaneously, the early-strength characteristics highly meet the rapid delivery requirements of winter construction and emergency repair projects. The rapidly forming dense matrix simultaneously imparts good initial impermeability to the structure, effectively preventing potential damage from early rainwater erosion and freeze-thaw cycles, creating significant economic value while improving the overall project progress efficiency.

[0012] 4. Good high-temperature resistance. The basalt fiber seawater sand concrete of the present invention can still maintain a high residual strength after being subjected to high temperatures of 200~800℃ (specifically 200℃, 400℃, 600℃ and 800℃) and then naturally cooled. Taking Example 4 as an example, after 200℃, the retention rates of cubic compressive strength, splitting tensile strength, and flexural strength were 104% (greater than 100%), 92% (greater than 90%), and 101.3% (greater than 100%), respectively; after 400℃, they were 90.9% (greater than 90%), 76% (greater than 75%), and 79.7% (greater than 79%); after 600℃, they were 62.9% (greater than 60%), 46% (greater than 45%), and 46.8% (greater than 45%); and after 800℃, they still reached 38.1% (greater than 35%), 22% (greater than 20%), and 27.8% (greater than 25%), all higher than the comparative example without basalt fiber. Under high temperature, the dehydration of cement stone, vaporization of pore water, and the difference in thermal deformation between aggregate and paste can induce the propagation of microcracks, leading to a decrease in concrete strength. Short-cut basalt fibers exhibit good thermal stability. When uniformly dispersed, they can form a fiber "bridging" network within the matrix, exerting tensile, constraining, and energy-dissipating effects on microcracks during heating and cooling, thus mitigating crack penetration and deterioration of the interface transition zone. This invention not only improves tensile and flexural strength at room temperature but also enhances the residual mechanical properties of concrete after exposure to fire or localized high temperatures, providing a more reliable material basis for the post-disaster assessment, repair, and continued service of marine engineering structures.

[0013] 5. Excellent adaptability to saline-alkali environments. The basalt fiber seawater sand concrete of this invention, prepared using seawater and sea sand as core raw materials, achieves the compressive strength standard of ordinary concrete of the same grade (C40), demonstrating its excellent adaptability to saline-alkali environments. Basalt fibers possess excellent chemical stability, forming a three-dimensional interwoven network structure after being uniformly dispersed in the concrete matrix. This effectively blocks the intrusion channels of harmful corrosive media such as chloride and sulfate ions in the seawater environment, optimizes the internal pore structure and interface transition zone of the concrete, improves the density of the matrix, and inhibits the loosening of the cementitious system caused by seawater components and the formation of magnesium silicate hydrates. This avoids the problem of significant strength reduction in concrete due to saline-alkali erosion, allowing the concrete to maintain a strength level comparable to ordinary concrete of the same grade while utilizing seawater and sea sand resources on-site. This fully demonstrates its excellent adaptability to saline-alkali environments and is suitable for the highly corrosive marine service environment. SEM test results are as follows: Figure 11 As shown, a relatively stable interfacial bond is formed between basalt fibers and hydration products. The fibers "bridge" microcracks and disrupt the pore connectivity path, reducing the risk of crack penetration and erosion medium infiltration at the microscopic level, and providing mechanistic support for the applicability to saline-alkali environments.

[0014] 6. Excellent workability. The basalt fiber-reinforced seawater sand concrete of this invention, with its large specific surface area and three-dimensional interwoven structure, provides appropriate physical constraint and surface adsorption for free water within the system, resulting in a stable and controllable adjustment of the mixture's flowability with increasing admixture dosage. Actual measurements of the slump in each embodiment show a range of 100mm to 190mm, which aligns with the core requirement in current concrete pumping construction technical specifications that the slump at the pump in pumping operations should generally not be lower than 100mm. The intervention of the micro-fiber network simultaneously imparts good cohesiveness and water retention to the slurry, reducing the segregation and bleeding risks that are prone to occur in conventional cast-in-place operations. The superior overall workability provides a solid material foundation for the pumping and casting of components. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0016] Figure 1 This is a schematic diagram of a device for measuring the slump of basalt fiber seawater sand concrete.

[0017] Figure 2 This is a schematic diagram of a testing device for the compressive, axial compressive, and splitting tensile strength of basalt fiber seawater sand concrete cubes.

[0018] Figure 3This is a schematic diagram of a fixture for testing the splitting tensile strength of basalt fiber seawater sand concrete; where A is the test block, B is the spacer strip, and C is the spacer block.

[0019] Figure 4 This is a schematic diagram of a basalt fiber seawater sand concrete flexural strength testing device.

[0020] Figure 5 This is a schematic diagram of a box-type resistance furnace for high-temperature processing.

[0021] Figure 6 The image shows the failure morphology of a cube of basalt fiber reinforced seawater sand concrete after the compressive strength test.

[0022] Figure 7 The image shows the failure morphology of a specimen after a splitting tensile strength test of basalt fiber seawater sand concrete.

[0023] Figure 8 The image shows the failure morphology of the specimen after the flexural strength test of basalt fiber seawater sand concrete.

[0024] Figure 9 The image shows the failure morphology of the specimen after the axial compressive strength test of basalt fiber seawater sand concrete.

[0025] Figure 10 SEM microstructure of the fiber bridging effect in basalt fiber seawater sand concrete prepared for the example.

[0026] Figure 11 SEM microstructure of the basalt fiber seawater sand concrete prepared for the example, showing its effect on improving pore connectivity and blocking ion erosion.

[0027] Figure 12 A comparison of the cubic compressive strength of basalt fiber seawater sand concrete prepared in different embodiments and seawater sand concrete prepared in the comparative example.

[0028] Figure 13 A comparison of the splitting tensile strength of basalt fiber seawater sand concrete prepared in different embodiments and seawater sand concrete prepared in the comparative example.

[0029] Figure 14 A comparison of the flexural strength of basalt fiber seawater sand concrete prepared in different embodiments and seawater sand concrete prepared in the comparative example.

[0030] Figure 15 A comparison of the axial compressive strength of basalt fiber seawater sand concrete prepared in different embodiments and seawater sand concrete prepared in the comparative example.

[0031] Figure 16The diagram shows a comparison of the cubic compressive strength of basalt fiber seawater sand concrete prepared in different embodiments after high temperature and seawater sand concrete prepared in the comparative example.

[0032] Figure 17 The figure shows a comparison of the splitting tensile strength of basalt fiber seawater sand concrete prepared in different embodiments after high temperature and seawater sand concrete prepared in the comparative example.

[0033] Figure 18 The image shows a comparison of the flexural strength of basalt fiber seawater sand concrete prepared in different embodiments after high temperature and seawater sand concrete prepared in the comparative example. Detailed Implementation

[0034] Terminology Explanation: SSC stands for Seawater Sand Concrete.

[0035] SSC-15 represents Example 3, where the fiber volume content is 0.15%.

[0036] SSC-20 represents Example 4, where the fiber volume content is 0.20%.

[0037] SSC-25 represents Example 5, where the fiber volume content is 0.25%.

[0038] To address the significant shortcomings of traditional concrete in applications such as shield tunnel segments, FRP concrete structures, and reinforcement and repair of existing concrete structures in marine environments, this invention develops a basalt fiber seawater sand concrete. By incorporating short-cut basalt fibers, the mechanical and corrosion-resistant properties of basalt fibers are fully utilized. Combined with the abundant seawater and sea sand resources in coastal areas, this invention achieves a synergistic improvement in the mechanical properties, durability, and environmental friendliness of marine concrete materials, possessing significant engineering application value and practical significance.

[0039] In existing technologies, glass fibers and polypropylene fibers are commonly incorporated to address the insufficient mechanical properties or durability of reinforced concrete (SSC). However, glass fibers have poor resistance to salt and alkali corrosion and are prone to alkali corrosion degradation with long-term use. While polypropylene fibers possess good resistance to salt and alkali corrosion, their elastic modulus is low (typically 3-4 GPa) and tensile strength is low (typically 0.5-0.7 GPa), limiting their ability to improve the flexural and tensile properties of concrete. Therefore, there is an urgent need to find new fibers to address the problem that conventional fiber-reinforced systems cannot simultaneously improve the mechanical properties of SSC and provide long-term resistance to salt and alkali corrosion.

[0040] The core innovation of this invention lies in introducing short-cut basalt fibers with specific parameters into a seawater sand concrete system, and achieving a balance between tensile strength, flexural strength, and workability by controlling their dosage. The dosage ranges of other components are set with slight fluctuations around the benchmark mix proportions of seawater sand concrete to ensure the fluidity, aggregate encapsulation, and strength grade stability of the mixture, and are not considered as independent variables. The embodiments provided by this invention have demonstrated the improving effect of basalt fiber on tensile and flexural properties through different dosages.

[0041] In addition, existing technologies also disclose the addition of basalt fibers to seawater sand concrete. However, this invention does not simply add basalt fibers as a conventional reinforcing component to seawater sand concrete. Instead, it achieves a significant improvement in splitting tensile strength and flexural strength under ordinary curing conditions by using mix design suitable for marine concrete, controlling the parameters of short-cut basalt fibers, and optimizing the fiber dispersion process. At the same time, it maintains good construction applicability and engineering economy.

[0042] For example, existing studies have disclosed the effect of basalt fiber on the performance of seawater sand concrete, but the optimal dosage of basalt fiber is 0.2%. The performance improvement is limited; the 28-day splitting tensile strength is only slightly higher than the un-fiber group, and the 28-day flexural strength shows a trend of first decreasing, then increasing, and finally stabilizing with increasing fiber dosage, indicating that the fiber reinforcement effect is insufficient. Furthermore, it is clearly pointed out that excessive fiber dosage easily leads to agglomeration and uneven dispersion within the concrete, resulting in a decrease in compressive strength. To address these problems, this invention uses short-cut basalt fibers with a length of 4-8 mm, and evenly distributes the fibers into the mixer using a 10-15 mm sieve during mixing, making it easier for the fibers to form a uniformly dispersed three-dimensional interwoven structure in the matrix. This process helps reduce fiber agglomeration and improves the stress transfer efficiency between the fiber and the cement matrix. In this invention, the 28-day splitting tensile strength increased from 3.6 MPa to 5.0 MPa, an increase of 38.9%; the 28-day flexural strength increased from 6.4 MPa to 7.9 MPa, an increase of 23.4%. Therefore, this invention significantly improves the tensile and flexural properties of seawater sand concrete and better reflects the technical contribution of basalt fiber in crack resistance and toughening. Furthermore, this invention uses 210 specimens, and the larger experimental scale allows for more thorough verification of performance changes under different fiber dosages, ages, and stress states, providing better data support for the obtained technical effects.

[0043] Existing technologies also disclose an alkali-resistant basalt fiber-reinforced seawater sand concrete. The disclosed technical solutions focus on preparing high-performance seawater sand concrete with a compressive strength exceeding 125 MPa, belonging to a high-strength, high-performance concrete system, which differs from the technical positioning of this invention, which targets C40 marine engineering concrete. The performance of the seawater sand concrete disclosed in the prior art relies on several high-cost or high-energy-consumption technical conditions, including using epoxy resin or vinyl ester resin as a film-forming agent to modify the basalt fiber surface, using a high proportion of microsilica powder, using a high dosage of water-reducing agent, and curing in a 90°C constant-temperature water bath for 48-72 hours after pouring. While these technical conditions are beneficial for obtaining high strength performance, they increase material costs, preparation energy consumption, and on-site construction difficulty. This invention, however, does not require resin film-forming modification of the basalt fiber, nor does it require 90°C constant-temperature water bath curing; good tensile and flexural strength enhancement effects can be obtained under ordinary standard curing conditions. Compared to conventional engineering construction environments, the preparation conditions of this invention are closer to those of traditional methods, avoiding the limitations imposed by high-temperature water bath curing on equipment, energy consumption, and component dimensions. This makes it more suitable for application in ready-mixed concrete, cast-in-place components, and general marine concrete engineering. Furthermore, existing publicly available technical solutions involve a relatively high dosage of water-reducing agent, typically 3% to 5% of the total mass of the cementitious material. Based on its preferred formulation, the water-reducing agent accounts for approximately 3.78% of the cementitious material mass. In contrast, the water-reducing agent dosage in this invention is 2.12 kg / m³. 3 The water-reducing agent content is approximately 0.50% of the cement mass. In existing publicly available technical solutions, the proportion of water-reducing agent in the preferred formulation is approximately 7.6 times that of this invention. If calculated according to the upper limit of 5% in existing publicly available technical solutions, it is close to 10 times that of this invention. High water-reducing agent content increases material costs and makes it more difficult to control the performance of the mixture. This invention can maintain a slump range of 100mm to 190mm with a lower water-reducing agent content, indicating that it has both mechanical strengthening effect and good workability. In addition, existing publicly available technical solutions also remove coarse aggregate and use a higher proportion of silica fume. Calculated according to its preferred formulation, the silica fume content is 10 parts, the total amount of cementitious material is 45 parts, and the silica fume accounts for 22.2% of the total amount of cementitious material. The price of silica fume is usually higher than that of ordinary cement, and a high amount of silica fume will increase the viscosity and cost of the mixture. In comparison, this invention retains the crushed stone skeleton, achieves the strength requirements of C40 marine concrete without relying on a high proportion of microsilica, and effectively improves splitting tensile strength and flexural strength, resulting in better material economy and engineering applicability.

[0044] The above comparison shows that while some existing technologies reveal that basalt fibers have a certain reinforcing effect on seawater sand concrete, the strength improvement is limited, and there is a problem of uneven fiber dispersion at high dosages. Other existing technologies can achieve high-performance concrete, but rely on resin modification of the fiber surface, high proportion of microsilica, high water-reducing agent dosage, and 90℃ water bath curing. Their application scenarios, material costs, and construction conditions differ from those of this invention. This invention, through a mix proportion suitable for C40 marine concrete, short-cut basalt fiber parameters, and a screening and dispersion process, effectively improves splitting tensile strength and flexural strength under ordinary curing conditions, while also considering workability, material costs, and engineering application value.

[0045] In one typical embodiment, the present invention provides a basalt fiber seawater sand concrete, which, by weight, is composed of the following components: 35-45 parts cement, 65-75 parts sea sand, 105-120 parts crushed stone, 15-20 parts seawater, 0.1-0.3 parts water-reducing agent, and 0.1-1 parts basalt fiber.

[0046] Furthermore, the composition includes 40-45 parts cement, 65-70 parts sea sand, 110-115 parts crushed stone, 15-20 parts seawater, 0.2-0.3 parts water-reducing agent, and 0.1-0.8 parts basalt fiber.

[0047] The mass fraction of basalt fiber can be 0.1 parts, 0.133 parts, 0.2 parts, 0.265 parts, 0.3 parts, 0.398 parts, 0.4 parts, 0.5 parts, 0.53 parts, 0.6 parts, 0.663 parts, 0.7 parts, 0.795 parts, 0.8 parts, 0.9 parts, or 1 part, etc. Alternatively, the amount of basalt fiber incorporated is 0.05% to 0.3% of the volume fraction of the concrete. For example, in the embodiments of this invention, Embodiments 3, 4, and 5 have better performance, with corresponding fiber fractions of 0.40 parts, 0.53 parts, and 0.663 parts, respectively; and corresponding fiber volume fractions of 0.15%, 0.20%, and 0.25%, respectively. Therefore, the preferred mass fraction of basalt fiber is 0.4 to 0.7 parts, or the fiber volume fraction is 0.15% to 0.25%.

[0048] The impact of different basalt fiber volume fractions on the results is mainly reflected in the differences in splitting tensile strength, flexural strength, and workability of concrete. Appropriate addition of basalt fiber can improve the tensile and flexural properties of concrete, but higher fiber content is not always better; excessive content can easily affect fiber dispersion and the workability of the mixture. Therefore, the fiber volume fraction range (0.05%~0.3%) in this invention actually includes all tried fiber fractions, with the optimal fraction mainly concentrated around 0.15%~0.20%.

[0049] In the seawater sand concrete provided by this invention, due to the presence of crushed stone coarse aggregate, the aggregate-paste interface is more prone to becoming a weak area for crack initiation and propagation, requiring basalt fibers to play a bridging and toughening role. Short-cut basalt fibers are uniformly distributed in the concrete, forming a fiber "bridging" network within it. During heating and cooling processes, this network exerts tensile, restraining, and energy-dissipating effects on microcracks. Specifically, the bridging effect of this invention is achieved by uniformly dispersing short-cut basalt fibers at a volume ratio of 0.05%~0.3% within the matrix formed by cement paste, sea sand, and crushed stone in C40 seawater sand crushed stone concrete. This creates restraint on both sides of the cracks, inhibiting crack propagation in the coarse aggregate-paste interface transition zone and around the aggregate, thereby significantly improving splitting tensile strength and flexural strength. Furthermore, short-cut basalt fibers increased the 28-day splitting tensile strength from 3.6 MPa to 5.0 MPa and the flexural strength from 6.4 MPa to 7.9 MPa, and SEM analysis demonstrated that the fibers formed bridging constraints on both sides of the crack.

[0050] Basalt fiber, as a novel inorganic environmentally friendly high-performance material, boasts a tensile strength exceeding 1000 MPa and an elastic modulus of 70-110 GPa, exhibiting mechanical properties far superior to polypropylene fiber. When incorporated into seawater sand concrete, it can inhibit the initiation and propagation of microcracks through a "bridging" effect, enhancing the tensile, flexural, and toughness of the concrete and addressing the issues of high matrix brittleness and weak mechanical properties. Compared to glass fiber, basalt fiber exhibits a more significant advantage in resisting seawater corrosion. Glass fiber is prone to chemical corrosion, surface deterioration, and strength reduction under the corrosive environments of seawater chloride ions, acids, and alkalis, resulting in poor long-term service stability. In contrast, basalt fiber possesses excellent chemical stability, effectively resisting the erosion of harmful media such as chloride and sulfate ions in seawater. It is not easily corroded or degraded, maintaining stable performance in concrete over a long period, thus improving the concrete's durability against ion penetration and salt corrosion. Furthermore, basalt fiber exhibits good thermal stability, maintaining a certain fiber morphology and reinforcing capacity even after exposure to high temperatures. When cement-based matrices are heated, hydration products dehydrate, pore water vaporizes, and interfacial thermal damage occurs. Uniformly dispersed short-cut basalt fibers can bridge and pull on microcracks induced by high temperatures, delaying crack penetration and mitigating the decline in compressive, splitting, tensile, and flexural strength after cooling. Furthermore, this fiber is naturally environmentally friendly, can be returned to nature after disposal, and has good compatibility with inorganic polymer cementitious materials. It can construct composite systems with high durability, high-temperature resistance, and environmental friendliness, effectively compensating for the shortcomings of polypropylene and glass fibers in mechanical properties, corrosion resistance, and residual mechanical properties after high temperatures. It is more suitable for marine engineering needs and can solve the key problem of poor mechanical properties and durability in traditional seawater and marine sand concrete.

[0051] Regarding the various components of this invention, exploratory tests were conducted on the remaining components during the preliminary experimental exploration phase. In a seawater sand concrete system, a group was prepared with fly ash and silica fume added, where fly ash was added at 10% of the mass of the cementitious material and silica fume at 5% of the mass of the cementitious material. The test results showed that the performance and mechanical properties of the mixture after adding fly ash and silica fume were quite similar to the baseline group without fly ash and silica fume, and did not demonstrate a significant advantage over existing embodiments.

[0052] The key technical focus of this invention lies in the improvement of the tensile, flexural, and crack-resistant toughening properties of seawater sand concrete by chopped basalt fibers. The embodiments provided by this invention demonstrate the influence of different basalt fiber dosages on slump, compressive strength, splitting tensile strength, flexural strength, and axial compressive strength. The effect of basalt fibers on improving splitting tensile strength and flexural strength is particularly evident. To avoid weakening the key technical solution of this invention by introducing mineral admixtures such as fly ash and silica fume, this invention chooses to use only cement as a binder, which is more conducive to highlighting the "bridging" toughening and crack-resistant effects of basalt fibers in seawater sand concrete.

[0053] Furthermore, silica fume is relatively expensive and has a certain impact on the water requirement and workability of the mixture. This invention does not use silica fume, which further reduces material costs while ensuring the mechanical and workability of the concrete, making this basalt fiber seawater sand concrete more suitable for large-scale application in coastal engineering projects.

[0054] Therefore, based on the above, the present invention ultimately adopts a single cementitious material system to highlight the reinforcing and toughening effect of basalt fiber, while also taking into account cost advantages.

[0055] In some embodiments of this implementation, the cement is P·O 42.5 ordinary Portland cement.

[0056] In some embodiments of this implementation, the fineness modulus of the sea sand is 2.2~2.6, and the apparent density is 2.5~2.7 g / cm³. 3 .

[0057] In some embodiments of this implementation, the crushed stone has a particle size of 5-16 mm, continuous gradation, a crushing index of 10%-18%, and a needle-like and flaky particle content of 4%-8%.

[0058] In some embodiments of this implementation, the seawater is natural seawater taken from coastal areas or artificial seawater prepared in accordance with ASTM D1141-98(2021) standard.

[0059] In some embodiments of this implementation, the water-reducing agent is a polycarboxylate high-performance water-reducing agent with a solid content of 35-40% and a water reduction rate of 25-30%.

[0060] In some embodiments of this implementation, the basalt fiber is chopped basalt fiber with a single filament diameter of 10-20 μm, a length of 4-8 mm, a tensile strength of 1000-1200 MPa, an elastic modulus of 72-78 GPa, and a density of 2.6-2.7 g / cm³. 3 .

[0061] Basalt fiber possesses excellent corrosion resistance, along with high strength and elastic modulus. When uniformly dispersed in a concrete matrix, it forms a three-dimensional interwoven network structure. When microcracks develop in concrete under tension or bending, it effectively bridges the cracks, transfers stress, and inhibits crack initiation and propagation, thereby improving the concrete's fracture energy, impact resistance, and toughness. It also disperses internal stress, alleviates stress concentration caused by drying shrinkage and temperature changes, and reduces early cracking. Furthermore, its corrosion resistance and resistance to degradation in harsh environments allow it to function stably for a long time. It effectively blocks the intrusion channels of harmful media such as chloride and sulfate ions, optimizes the internal pore structure and interface transition zone, increases matrix density, resists environmental damage such as salt corrosion, and delays steel corrosion and matrix performance deterioration. Under high temperatures, the internal temperature gradient and differences in thermal expansion of the concrete can easily damage the interface between the paste and aggregate. The fiber network can disperse stress at the crack tip and dissipate some energy through pull-out, slippage, and interfacial bonding, making the crack propagation path more tortuous and helping to improve the remaining load-bearing capacity after cooling. Short-cut fibers, with their shorter length and better dispersion, can form local constraints in many weak areas, which is particularly beneficial for maintaining splitting tensile strength and flexural strength after high temperatures. This improves the long-term durability and post-disaster service safety of concrete from both the material itself and structural perspectives. The synergistic effect of toughening, crack resistance, durability, and improved residual mechanical properties after high temperatures allows concrete to maintain good ductility and stability under dynamic loads and harsh environments, making it widely applicable in fields such as pavement, bridges, seismic structures, and marine engineering.

[0062] In one typical embodiment, the present invention provides a method for preparing the above-mentioned basalt fiber seawater sand concrete, comprising the following steps: Cement, sea sand, and crushed stone are dry-mixed to obtain dry material; water-reducing agent is dissolved in seawater to obtain mixed solution; the mixed solution and dry material are mixed and stirred, and then basalt fiber is added and stirred; after stirring, it is poured into mold, and after demolding, it is cured according to standard to the specified age.

[0063] The preparation steps of the dry material and the mixed solution can be carried out simultaneously or sequentially, and no specific limitation is made in this invention.

[0064] In some embodiments of this implementation, the dry mixing process takes 1 to 5 minutes, preferably 1 to 2 minutes. The stirring speed is not specifically limited; for example, during the dry mixing process, the stirring speed is 45 to 60 r / min.

[0065] In some embodiments of this implementation, the mixed solution and dry materials are stirred for 2-10 minutes, preferably 3-4 minutes, until the concrete mixture becomes fluid. The stirring speed is not specifically limited; for example, during mixing, the stirring speed is 45-60 r / min.

[0066] In some embodiments of this implementation, the basalt fiber is added by vibrating a vibrating screen. The basalt fiber is placed in the screen, and the screen is shaken while stirring to ensure the fiber is evenly distributed into the stirring device. Stirring is performed for 1-5 minutes (preferably 2-3 minutes) until the fiber is evenly dispersed. The stirring speed is not specifically limited, such as 45-60 r / min.

[0067] In some embodiments of this implementation, after mixing, standard curing can be performed. Specifically: the mixture is placed in a mold, vibrated and leveled, left to stand at room temperature for 24-48 hours, then demolded, and subsequently placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of not less than 95% for curing to the specified age.

[0068] In a preferred embodiment, the method for preparing basalt fiber seawater sand concrete includes the following steps: S1. Pour the weighed cement, sea sand and gravel into the mixer and dry mix for 1~2 minutes; S2. Add the weighed water-reducing agent to the weighed seawater and dissolve it. S3. Add the solution obtained in S2 to the dry material mixed in S1, and then use a mixer to mix for 3-4 minutes until the concrete mixture is fluid. S4. Place the weighed basalt fiber into a sieve with a aperture of 10-15mm, restart the mixer, and shake the sieve rapidly during mixing to ensure that the fiber is evenly distributed into the mixer. Mix for 2-3 minutes until the fiber is evenly dispersed. After mixing, basalt fiber seawater sand concrete is obtained.

[0069] Preferably, in S1, the mixer speed is 45~60 r / min. In S3, the mixer speed is 45~60 r / min. In S4, the mixer speed is 45~60 r / min.

[0070] In one typical embodiment, the present invention provides the application of the above-mentioned basalt fiber seawater sand concrete or the basalt fiber seawater sand concrete prepared by the above preparation method. The application includes, but is not limited to: application in crack resistance and toughening of shield tunnel segments in coastal tunnels, or application in fiber reinforced polymer (FRP) concrete structures, or application in reinforcement, repair and durability improvement of existing concrete structures in marine environments.

[0071] The slump of the basalt fiber seawater sand concrete is maintained in the range of 100mm to 190mm.

[0072] The 3-day cube compressive strength is greater than 30.5 MPa, preferably greater than 31 MPa. The 7-day cube compressive strength is greater than 35 MPa, preferably greater than 36 MPa. The 28-day cube compressive strength is greater than 45 MPa, preferably greater than 47 MPa, and more preferably greater than 49.5 MPa.

[0073] The 3-day splitting tensile strength is greater than 2.8 MPa, preferably greater than 3 MPa, and more preferably greater than or equal to 3.4 MPa. The 7-day splitting tensile strength is greater than 3 MPa, preferably greater than 3.3 MPa. The 28-day splitting tensile strength is greater than 3.6 MPa, preferably greater than or equal to 5 MPa.

[0074] The 3-day flexural strength is greater than 5 MPa, preferably greater than or equal to 5.7 MPa. The 7-day flexural strength is greater than 5.5 MPa, preferably greater than or equal to 6 MPa. The 28-day flexural strength is greater than 6.4 MPa, preferably greater than 7 MPa, and more preferably greater than or equal to 7.5 MPa.

[0075] The axial compressive strength is ≥41MPa, preferably 41~45MPa.

[0076] After 200℃, the retention rates of the cube's compressive strength, splitting tensile strength, and flexural strength are greater than 100%, greater than 84% (preferably greater than 90%), and greater than 97% (preferably greater than 100%), respectively; after 400℃, they are greater than 80% (preferably greater than 90%), greater than 64% (preferably greater than 75%), and greater than 69% (preferably greater than 79%), respectively; after 600℃, they are greater than 45% (preferably greater than 60%), greater than 35% (greater than 45%), and greater than 31% (preferably greater than 45%), respectively; and after 800℃, they still reach greater than 25% (preferably greater than 35%), greater than 12% (preferably greater than 20%), and greater than 17% (preferably greater than 25%), respectively.

[0077] Seawater and sea sand concrete can make full use of the abundant seawater and sea sand resources in coastal areas. This not only significantly reduces the transportation costs of freshwater river sand and minimizes the damage to river ecosystems caused by inland sand mining, but also optimizes the internal density of the sea sand through the micro-aggregate effect of shell fragments. Furthermore, the presence of Cl- in seawater further enhances its properties. - SO4 2- The early acceleration of cement hydration enhances its compressive strength compared to ordinary concrete of the same strength grade, thus demonstrating significant economic and construction efficiency advantages in marine engineering projects such as sea-crossing bridges and breakwaters. Furthermore, the natural compatibility of seawater and sea sand with the marine environment prevents structural erosion caused by osmotic pressure differences, and its erosion resistance effectively resists tidal scouring, thereby extending the service life of marine structures.

[0078] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0079] The present invention will be further described below with reference to the embodiments.

[0080] In the following embodiments: The cement was Conch brand P·O 42.5 ordinary Portland cement, purchased from Anhui Xuancheng Conch Cement Co., Ltd.

[0081] The fineness modulus of sea sand is 2.2~2.6, and the apparent density is 2.5~2.7 g / cm³. 3 It originates from the Yellow Sea coast of Qingdao.

[0082] The crushed stone has a particle size of 5~16mm, continuous gradation, a crushing index of 16%, and a needle-like and flaky particle content of 4%. It was purchased from Jinan Jianyuan Building Materials Co., Ltd.

[0083] The seawater was artificial seawater prepared in accordance with the ASTM D1141-98(2021) standard.

[0084] The water-reducing agent is a high-performance polycarboxylate water-reducing agent with a solid content of 35-40% and a water reduction rate of 25-30%, purchased from Shanxi Feike New Material Technology Co., Ltd.

[0085] The fiber is chopped basalt fiber, with a single filament diameter of 10~20 μm, a length of 4~8 mm, a tensile strength of 1000~1200 MPa, an elastic modulus of 72~78 GPa, and a density of 2.6~2.7 g / cm³. 3 .

[0086] When concrete is modified by adding fibers, the fiber dosage is usually expressed as volumetric dosage to reflect the spatial distribution and "bridging" reinforcement effect of the fibers within a unit volume of concrete. Therefore, in this invention, it is more appropriate to express the chopped basalt fiber dosage as volumetric dosage. In the following experiments, the volumetric dosage of chopped basalt fiber (fiber volume per 1 m³) is... 3 The method for calculating the proportion of concrete is as follows: The fiber density is taken as 2650 kg / m³. 3 As in Example 1, the calculated dosage is 1.33 / 2650 × 100% = 0.05%.

[0087] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0088] Example 1: In a specific embodiment of the basalt fiber seawater sand concrete of the present invention, the components required to prepare each cubic meter of the concrete include: 424 kg of cement, 682 kg of sea sand, 1114 kg of crushed stone, 169 kg of seawater, 2.12 kg of water-reducing agent, and 1.33 kg of short-cut basalt fiber (volume admixture 0.05%).

[0089] The preparation method of basalt fiber seawater sand concrete includes the following steps: S1. Pour the weighed cement, sea sand and gravel into the mixer and dry mix for 1~2 minutes; S2. Add the weighed water-reducing agent to the weighed seawater and dissolve it. S3. Add the solution obtained in S2 to the dry material mixed in S1, and then use a mixer to mix for 3-4 minutes until the concrete mixture is fluid. S4. Place the weighed basalt fiber in a sieve with a aperture of 10-15mm, restart the mixer, and shake the sieve rapidly during mixing to ensure that the fiber is evenly distributed into the mixer. Mix for 2-3 minutes until the fiber is evenly dispersed. After mixing, pack the mixture into a mold, vibrate it, and smooth it. Let it stand at room temperature for about 24 hours before removing it from the mold. Then place it in a standard curing room with a temperature of 20±2℃ and a relative humidity of not less than 95% to cure it to the specified age.

[0090] Example 2: The difference from Example 1 is that 0.10% of short-cut basalt fibers were added by volume; all other aspects are the same as in Example 1. Specifically: In a specific embodiment of the basalt fiber seawater sand concrete of the present invention, the components required to prepare each cubic meter of the concrete include: 424 kg of cement, 682 kg of sea sand, 1114 kg of crushed stone, 169 kg of seawater, 2.12 kg of water-reducing agent, and 2.65 kg of short-cut basalt fiber (volume admixture 0.10%).

[0091] Example 3: The difference from Example 1 is that 0.15% of short-cut basalt fibers were added by volume; all other aspects are the same as in Example 1. Specifically: In a specific embodiment of the basalt fiber seawater sand concrete of the present invention, the components required to prepare each cubic meter of the concrete include: 424 kg of cement, 682 kg of sea sand, 1114 kg of crushed stone, 169 kg of seawater, 2.12 kg of water-reducing agent, and 3.98 kg of short-cut basalt fiber (volume admixture of 0.15%).

[0092] Example 4: The difference from Example 1 is that 0.20% of short-cut basalt fibers were added by volume; all other aspects are the same as in Example 1. Specifically: In a specific embodiment of the basalt fiber seawater sand concrete of the present invention, the components required to prepare each cubic meter of the concrete include: 424 kg of cement, 682 kg of sea sand, 1114 kg of crushed stone, 169 kg of seawater, 2.12 kg of water-reducing agent, and 5.30 kg of short-cut basalt fiber (volume admixture 0.20%).

[0093] Example 5: The difference from Example 1 is that 0.25% of short-cut basalt fibers were added by volume; all other aspects are the same as in Example 1. Specifically: In a specific embodiment of the basalt fiber seawater sand concrete of the present invention, the components required to prepare each cubic meter of the concrete include: 424 kg of cement, 682 kg of sea sand, 1114 kg of crushed stone, 169 kg of seawater, 2.12 kg of water-reducing agent, and 6.63 kg of short-cut basalt fiber (volume admixture 0.25%).

[0094] Example 6: The difference from Example 1 is that 0.30% of short-cut basalt fibers were added by volume; all other aspects are the same as in Example 1. Specifically: In a specific embodiment of the basalt fiber seawater sand concrete of the present invention, the components required to prepare each cubic meter of the concrete include: 424 kg of cement, 682 kg of sea sand, 1114 kg of crushed stone, 169 kg of seawater, 2.12 kg of water-reducing agent, and 7.95 kg of short-cut basalt fiber (volume admixture 0.30%).

[0095] Comparative Example 1: The conventional seawater and sea sand concrete of the present invention serves as a comparative example. The components required to prepare one cubic meter of this concrete include: 424 kg of cement, 682 kg of sea sand, 1114 kg of crushed stone, 169 kg of seawater, and 2.12 kg of water-reducing agent.

[0096] The conventional method for preparing seawater sand concrete includes the following steps: S1. Pour the weighed cement, sea sand and gravel into the mixer and dry mix for 1~2 minutes; S2. Add the weighed water-reducing agent to the weighed seawater and dissolve it. S3. Add the solution obtained in S2 to the dry material mixed in S1, and then use a mixer to mix for 3-4 minutes until the concrete mixture is fluid. After mixing, put the mixture into the mold, vibrate and smooth it. After standing at room temperature for about 24 hours, remove the mold and then place it in a standard curing room with a temperature of 20±2℃ and a relative humidity of not less than 95% to cure for the specified age.

[0097] Liquidity effect verification: According to the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T 50080-2016), the inner wall of the slump test cylinder and the test base plate were first moistened, and the cylinder was placed in the center of the base plate and fixed. Concrete from Examples 1 to 6 and Comparative Example 1 was filled into the cylinder in three layers, each layer occupying approximately 1 / 3 of the cylinder height. Each layer was tamped 25 times in a spiral motion from the outside to the inside using a tamping rod. After the top layer was filled and smoothed, the slump test cylinder was lifted vertically and smoothly within 3-7 seconds. After the concrete stopped slumping, the height difference between the cylinder height and the highest point of the specimen after slumping was measured to obtain the slump values ​​for Examples 1 to 6 and Comparative Example 1, respectively. The entire test process was completed within 150 seconds. The slump test results are shown in Table 1.

[0098] Table 1. Slump test results of basalt fiber reinforced seawater sand concrete

[0099] With the increase of basalt fiber content, the concrete slump in each embodiment showed a steady decreasing trend from 190mm to 100mm. This rheological characteristic mainly stems from the three-dimensional interwoven network constructed by the fibers within the matrix. Due to its large specific surface area, the basalt fibers, after uniform dispersion, moderately encapsulate and adsorb free water within the system, resulting in a controllable and moderate increase in the frictional resistance within the mixture. This physical intervention at the microstructure level did not impair the effective deformation capacity of the slurry; the measured slump remained above the industry standard lower limit of 100mm, effectively meeting the basic fluidity requirements of conventional pumping operations. The moderate yield stress imparted by the interwoven fiber network effectively restrained the tendency of coarse aggregate to sink and water to rise, preventing the risks of bleeding and segregation that are prone to occur during the pouring stage. This positive optimization of the slurry's cohesiveness and water retention ensures that the concrete, while meeting construction specifications, also possesses good overall workability, effectively supporting efficient pumping and casting on-site.

[0100] Mechanical performance verification: According to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019), basalt fiber reinforced seawater sand concrete prepared based on Examples 1 to 6 and Comparative Example 1 was poured into molds of 150mm×150mm×150mm, 100mm×100mm×100mm, 100mm×100mm×300mm, and 100mm×100mm×400mm. After compaction, the molds were covered with plastic film and cured in a standard concrete curing room for 24 hours before demolding. The specimens were then cured to the target age at a relative humidity of 95% and a temperature of 20±2℃. The cube compressive strength, splitting tensile strength, flexural strength, and axial compressive strength of the seven groups of basalt fiber reinforced seawater sand concrete specimens from Examples 1 to 6 and Comparative Example 1 were tested. The mechanical property test results are shown in Tables 2, 3, 4, and 5.

[0101] Table 2. Test results of compressive strength of basalt fiber reinforced seawater sand concrete cubes

[0102] Table 3. Test results of splitting tensile strength of basalt fiber reinforced seawater sand concrete

[0103] Table 4. Flexural strength test results of basalt fiber reinforced seawater sand concrete

[0104] Table 5. Test results of axial compressive strength of basalt fiber reinforced seawater sand concrete

[0105] Mechanical testing results show that the addition of short-cut basalt fibers significantly improves the splitting tensile strength and flexural strength of concrete, while the compressive strength remains relatively stable. This is mainly because the short-cut basalt fibers, when uniformly dispersed in the concrete matrix, can bear part of the tensile stress during loading and achieve stress transfer through the interfacial bonding between the fibers and the mortar. When microcracks appear inside the matrix, the fibers provide "bridging" constraints on both sides of the crack, slowing down the crack propagation rate and reducing local stress concentration, thereby improving the tensile and flexural strength and deformation compatibility of the concrete.

[0106] Mechanical strength testing only reflects macroscopic load-bearing results. Further explanation of the improved tensile and flexural properties requires consideration of fiber dispersion, interfacial bonding, and pore and crack morphology. Representative fractured specimens after 28 days of mechanical testing were taken, avoiding obvious crushing areas, and cut into approximately 5mm × 5mm × 5mm pieces. After hydration termination with anhydrous ethanol, low-temperature drying, and gold sputtering, hydration products, fiber-slurry interface, pore and microcrack morphology were observed using a Gemini SEM300 field emission scanning electron microscope. This provides microscopic evidence for the mechanical property test results. The microscopic test results are as follows: Figure 10 and Figure 11 As shown.

[0107] To further verify the residual mechanical properties of the basalt fiber seawater sand concrete of this invention after fire or high-temperature exposure, based on the above-mentioned room-temperature mechanical property tests, specimens from Examples 1 to 6 and Comparative Example 1, cured for 28 days, were subjected to high-temperature treatment, and cubic compressive strength, splitting tensile strength, and flexural strength tests were conducted after cooling. The furnace temperature control, furnace temperature monitoring, and heating uniformity control during the high-temperature treatment process were performed in accordance with the relevant requirements of "Test Methods for Fire Resistance of Building Components Part 1: General Requirements" (GB / T 9978.1-2008). The mechanical property tests after cooling were conducted according to the provisions of "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019).

[0108] Before high-temperature treatment, specimens that had reached the specified curing age were placed in a well-ventilated and dry environment to allow for moderate moisture loss from the surface, thus reducing the impact of concentrated internal water vapor pressure on the test results during the heating process. The specimens were placed in a box-type resistance furnace, with appropriate spacing maintained between specimens and between the specimens and the furnace walls to ensure relatively uniform heating. The high-temperature treatment temperatures were set at 200℃, 400℃, 600℃, and 800℃, with 28-day-old specimens that had not undergone high-temperature treatment serving as a 25℃ control group. During the heating process, thermocouples inside the furnace were used to monitor the temperature, and the temperature was increased to the target temperature according to the set heating regime. After reaching the target temperature, the temperature was held for 2 hours to allow the internal and external temperatures of the specimens to stabilize. After the holding period, the heating device was turned off, and the specimens were removed and allowed to cool naturally to 25±2℃ in a room temperature environment. The specimens after high-temperature treatment and cooling were then tested for cubic compressive strength, splitting tensile strength, and flexural strength to obtain the residual mechanical properties after different temperatures. The results of the mechanical property tests after high-temperature treatment are shown in Tables 6, 7, and 8.

[0109] Table 6. Test results of cubic compressive strength of basalt fiber reinforced seawater sand concrete after high temperature.

[0110] Table 7. Results of high-temperature splitting tensile strength test of basalt fiber reinforced seawater sand concrete

[0111] Table 8. Test results of flexural strength of basalt fiber reinforced seawater sand concrete after high temperature.

[0112] The smaller increase in strength at 7 days compared to 3 days for seawater-sand concrete indicates faster early strength development. This is because the chloride and sulfate ions in seawater promote the early dissolution and hydration of cement clinker minerals, accelerate the reaction process of aluminate and silicate phases, and promote the early formation of related hydration products. The early-formed hydrated calcium sulfoaluminate (AFt) and complex salt products have a certain filling effect on capillary pores, which is conducive to the formation of a relatively stable load-bearing structure in the matrix within a short period of time, thus enabling the material to achieve higher strength earlier.

[0113] The introduction of basalt fibers further improved the pore structure and interfacial transition zone of seawater sand concrete. For example... Figure 10 As shown, chopped fibers are dispersed in the cement matrix and form a relatively stable interface bond with the surrounding hydration products. When the matrix is ​​subjected to stress and microcracks are generated, the fibers can cross the two sides of the crack to form a "bridging" constraint, bearing part of the tensile stress and transferring the load, delaying crack propagation, and supporting the improvement of tensile and flexural strength at the microscopic level. Figure 11As shown, the fiber network also disrupts the connectivity paths of pores and microcracks, reducing the ease with which corrosive components such as chloride and sulfate ions migrate into the matrix, and mitigating the adverse effects of loosening of the cementitious system under salt conditions. Basalt fibers themselves possess good chemical stability and can maintain their reinforcing effect even in saline-alkali environments, enabling the concrete to achieve the strength requirements of ordinary concrete of the same grade even when using seawater and sea sand as raw materials, and demonstrating good resistance to ion erosion. After high-temperature treatment, the dehydration of the paste and the difference in thermal deformation between aggregates and paste easily induce microcracks and interface deterioration. Short-cut basalt fibers, with their good thermal stability and interfacial bonding effect, can "bridge" cracks, transfer tensile stress, and limit crack penetration, maintaining high levels of residual compressive, splitting tensile, and flexural strength after cooling. In summary, the addition of short-cut basalt fibers not only provides toughening and crack resistance but also has a certain slowing effect on salt and alkali erosion and performance degradation after high temperatures.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A basalt fiber-reinforced seawater sand concrete, characterized in that, By weight, it consists of the following components: 35-45 parts cement, 65-75 parts sea sand, 105-120 parts crushed stone, 15-20 parts seawater, 0.1-0.3 parts water-reducing agent, and 0.1-1 parts basalt fiber. The basalt fiber is a short-cut basalt fiber with a single filament diameter of 10-20 μm, a length of 4-8 mm, a tensile strength of 1000-1200 MPa, an elastic modulus of 72-78 GPa, and a density of 2.6-2.7 g / cm³. 3 ; Short-cut basalt fibers are evenly distributed in concrete and form a fiber bridging network inside it; The preparation method of the basalt fiber seawater sand concrete includes the following steps: Cement, sea sand, and crushed stone are dry-mixed to obtain dry material; water-reducing agent is dissolved in seawater to obtain mixed solution; the mixed solution and dry material are mixed and stirred, and then basalt fiber is added and stirred; after stirring, it is poured into mold, and after demolding, it is cured according to standard to the specified age.

2. The basalt fiber seawater sand concrete according to claim 1, characterized in that, 40-45 parts cement, 65-70 parts sea sand, 110-115 parts crushed stone, 15-20 parts seawater, 0.2-0.3 parts water-reducing agent, and 0.1-0.8 parts basalt fiber.

3. The basalt fiber seawater sand concrete according to claim 1 or 2, characterized in that, The cement includes P·O 42.5 ordinary Portland cement.

4. The basalt fiber seawater sand concrete according to claim 1 or 2, characterized in that, The sea sand has a fineness modulus of 2.2 to 2.6 and an apparent density of 2.5 to 2.7 g / cm³. 3 .

5. The basalt fiber seawater sand concrete according to claim 1 or 2, characterized in that, The crushed stone has a particle size of 5-16 mm, a crushing index of 10%-18%, and a needle-like and flaky particle content of 4%-8%.

6. The basalt fiber seawater sand concrete according to claim 1 or 2, characterized in that, The water-reducing agent is a polycarboxylate high-performance water-reducing agent with a solid content of 35-40% and a water reduction rate of 25-30%.

7. A method for preparing basalt fiber seawater sand concrete according to any one of claims 1 to 6, characterized in that, Includes the following steps: Cement, sea sand, and crushed stone are dry-mixed to obtain dry material; water-reducing agent is dissolved in seawater to obtain mixed solution; the mixed solution and dry material are mixed and stirred, and then basalt fiber is added and stirred; after stirring, it is poured into mold, and after demolding, it is cured according to standard to the specified age.

8. The preparation method according to claim 7, characterized in that, Dry mix for 1-5 minutes; Mix the solution and dry materials together for 2-10 minutes.

9. The preparation method according to claim 7, characterized in that, Basalt fiber is added by vibrating a vibrating screen; After adding basalt fiber, stir for 1-5 minutes.

10. The application of basalt fiber seawater sand concrete according to any one of claims 1 to 6 or basalt fiber seawater sand concrete prepared by the preparation method according to any one of claims 7 to 9, characterized in that, The applications include crack resistance and toughening of shield tunnel segments in coastal areas, or fiber-reinforced composite concrete structures, or reinforcement, repair and durability enhancement of existing concrete structures in marine environments.

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