A high impermeability concrete for marine environments and its preparation method

Abstract

This invention provides a high-permeability concrete for marine environments and its preparation method. The high-permeability concrete comprises the following components in parts by weight: 480-550 parts cementitious material; 650-750 parts fine aggregate; 1050-1150 parts coarse aggregate; 150-165 parts water; 3.84-8.25 parts polycarboxylate superplasticizer; 9.6-16.5 parts internally adsorbed cement-based penetrating crystallizing material; 2-4 parts nano-modified water-repellent agent; 0.096-0.55 parts graphene oxide dispersion; and 1-3 parts reinforcing fiber. The amount of the graphene oxide dispersion is measured according to the solid content of graphene oxide. The concrete provided by this application can effectively resist chloride and sulfate corrosion in underground structures in marine environments. Chloride ions have difficulty reaching the surface of the reinforcing steel, significantly delaying steel corrosion and thus significantly extending the service life of the concrete.

Description

Technical Field

[0001] This application relates to the field of concrete, and more specifically, to a high impermeability concrete for marine environments and a method for preparing the same. Background Technology

[0002] Underground concrete structures in marine environments face extremely harsh service conditions, primarily subjected to the combined effects of multiple adverse factors such as chloride erosion, sulfate corrosion, wet-dry cycles, and freeze-thaw damage. Among these, chloride ion-induced steel corrosion is the most significant cause of premature failure in marine concrete structures. While traditional marine concrete has improved impermeability to some extent, it still suffers from the following shortcomings: single mineral admixtures are difficult to form a dense pore structure, resulting in limited resistance to chloride ion penetration; early shrinkage cracking is a prominent issue, with cracks becoming channels for rapid chloride ion penetration; there is a lack of active protection mechanisms, leading to rapid deterioration of durability once microcracks appear; and the heat of hydration caused by high cement content is particularly prominent in large-volume structures. Summary of the Invention

[0003] This application provides a high impermeability concrete for marine environments and its preparation method, which can extend the service life of marine concrete.

[0004] Specifically, this application is implemented through the following technical solution: One aspect of this application provides a high impermeability concrete for marine environments, comprising the following components in parts by weight: 480-550 parts of cementitious material; 650-750 parts of fine aggregate; 1050-1150 parts coarse aggregate; 150-165 parts water; Polycarboxylate superplasticizer, 3.84–8.25 parts; 9.6–16.5 parts of internally adsorbed cement-based penetrating crystallizing material; 2-4 parts of nano-modified hydrophobic agent; 0.096–0.55 parts of graphene oxide dispersion; 1 to 3 parts of reinforcing fiber; wherein, the amount of components in the graphene oxide dispersion is measured according to the solid content of graphene oxide.

[0005] Optionally, the cementitious material comprises the following components in parts by weight: 40-60 parts silicate cement, 20-30 parts ultrafine slag powder, 5-10 parts silica fume, 5-15 parts calcined metakaolin, and 5-10 parts fly ash microspheres.

[0006] Optionally, the ultrafine slag powder has a specific surface area ≥800m² / kg, the silica fume has a SiO2 content ≥90% and a specific surface area ≥15000m² / kg, the calcined metakaolin has an activity index ≥110%, and the fly ash microspheres have a particle size ≤5μm.

[0007] Optionally, the nano-modified hydrophobic agent is a composite system formed by combining silane nanoemulsion, calcium stearate and nano silica; Based on the total mass of the composite system, the doping amount of nano-silica is 5% to 10%, wherein the particle size of the nano-silica is 20 to 50 nm.

[0008] Optionally, the concentration of the graphene oxide dispersion is 5-10 mg / mL, the graphene oxide sheet diameter is 1-5 μm, and the carbon-to-oxygen ratio is 2.0-2.5.

[0009] Optionally, the reinforcing fiber is basalt fiber or modified polypropylene fiber, with a length of 12-18 mm, a diameter of 15-25 μm, and an elastic modulus ≥40 GPa.

[0010] Optionally, the primary impermeability pressure of the internally incorporated cement-based permeable crystallizing material is ≥2.0MPa, and the secondary impermeability pressure is ≥1.8MPa.

[0011] Another aspect of this application provides a method for preparing high impermeability concrete in a marine environment as described in any of the above claims, comprising the following steps: S1. Mix the graphene oxide dispersion, 50% of the total water volume with the polycarboxylate superplasticizer, and ultrasonically disperse for 5-10 minutes to obtain a graphene oxide predispersant. S2. The internally mixed cement-based penetrating crystallizing material and the nano-modified water-repellent agent are dry-mixed evenly to obtain a functional component premix. S3. The silicate cement, the ultrafine slag powder, the silica fume, the calcined metakaolin, and the fly ash microspheres are mixed in proportion to obtain a composite cementitious material. S4. Add the coarse aggregate, the fine aggregate and the reinforcing fiber into the mixer and dry mix for 30-60 seconds. S5. Add the composite cementitious material and the functional component premix, and continue dry mixing for 30-60 seconds. S6. Add the remaining water and the graphene oxide pre-dispersion liquid, and stir for 150-210 seconds to obtain the concrete mixture.

[0012] Optionally, in step S1, the power of ultrasonic dispersion is 1.5 to 3 kW and the frequency is 15 to 24 kHz.

[0013] This application provides a high-permeability concrete for marine environments and a method for its preparation. The high-permeability concrete provided by this application has at least the following technical advantages: (1) The internally adsorbed cement-based penetrating crystalline material is uniformly distributed inside the concrete. When microcracks form in the concrete and water seeps in, the active chemical substances in the material dissolve and react to form insoluble crystals, which automatically fill and seal the cracks, preventing further penetration of water and chloride ions. This function solves the problem that cracks in traditional concrete become seepage channels, enabling the concrete to maintain its impermeability for a long time during its service life.

[0014] (2) The nano-modified water-repellent agent makes the pores inside the concrete hydrophobic, significantly reducing the water absorption rate and water absorption capacity of the concrete. Water is difficult to penetrate into the concrete, thereby reducing the carriers of harmful substances such as chloride ions and sulfate ions that migrate with water. This water-repellent agent works together with the above-mentioned cement-based penetrating crystallizing material to form a dual protection that reduces water ingress and blocks existing cracks.

[0015] (3) After the graphene oxide dispersion is mixed with the cementitious material, the graphene oxide can promote the more uniform and denser generation of cement hydration products, reduce the pores and microcracks inside the concrete, thereby improving the compressive strength and impermeability of the concrete.

[0016] (4) The reinforcing fibers are evenly distributed in the concrete, effectively restraining the cracks generated during plastic shrinkage and drying shrinkage. The fibers and graphene oxide jointly control the cracks at the macro and nano scales, respectively, thus comprehensively improving the crack resistance and toughness of the concrete.

[0017] (5) In underground structures in marine environments, concrete can effectively resist chloride erosion, sulfate corrosion, wet-dry cycles, and freeze-thaw damage. Chloride ions have difficulty reaching the surface of steel bars, thus significantly delaying steel corrosion; sulfate crystallization and expansion are less likely to cause cracking; and the lower water absorption rate weakens the destructive effects of freeze-thaw cycles. Ultimately, the service life of concrete is significantly extended compared to traditional marine concrete. Detailed Implementation

[0018] The technical solution of the present invention will be explained in detail below with reference to several representative embodiments.

[0019] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples and comparative examples are commercially available.

[0020] This application provides a high-permeability concrete for marine environments, comprising the following components in parts by weight: 480-550 parts of cementitious material; 650-750 parts of fine aggregate; 1050-1150 parts of coarse aggregate; 150-165 parts of water; 3.84-8.25 parts of polycarboxylate superplasticizer; 9.6-16.5 parts of internally adsorbed cementitious penetrating crystallizing material; 2-4 parts of nano-modified water-repellent agent; 0.096-0.55 parts of graphene oxide dispersion; and 1-3 parts of reinforcing fiber; wherein the amount of the components in the graphene oxide dispersion is measured according to the solid content of graphene oxide.

[0021] Experiments have verified that the graphene oxide dispersion selected in this application has good compatibility with the polycarboxylate superplasticizer. No precipitation, flocculation or gelation occurred after mixing, and it can be directly ultrasonically dispersed.

[0022] The internally incorporated cement-based penetrating crystalline material is uniformly distributed within the concrete. When microcracks form in the concrete and encounter seeping water, the active chemicals in this material dissolve and react to form insoluble crystals, automatically filling and sealing the cracks and preventing further penetration of water and chloride ions. This function solves the problem that cracks in traditional concrete become seepage channels, enabling the concrete to maintain its impermeability over a long period of service.

[0023] Nano-modified water-repellent agents impart hydrophobic properties to the pores within concrete, significantly reducing the water absorption rate and concentration. Water struggles to penetrate the concrete, thus reducing the carriers of harmful substances such as chloride and sulfate ions that migrate with water. This water-repellent agent, working in conjunction with the aforementioned cement-based penetrating crystalline materials, forms a dual protection against water ingress and the formation of existing cracks.

[0024] When graphene oxide dispersions are mixed with cementitious materials, graphene oxide promotes the more uniform and dense formation of cement hydration products, reducing porosity and microcracks within the concrete, thereby improving the compressive strength and impermeability of the concrete. Using polycarboxylate superplasticizers and appropriate ultrasonic-assisted dispersion can effectively improve the dispersion performance of graphene oxide dispersions and enhance the long-term stability of the dispersion system.

[0025] The reinforcing fibers are uniformly distributed throughout the concrete, effectively restraining cracks generated during plastic shrinkage and drying shrinkage. The fibers and graphene oxide jointly control cracking at both the macroscopic and nanoscale levels, comprehensively improving the crack resistance and toughness of the concrete. In summary, in underground structures within marine environments, this concrete effectively resists chloride erosion, sulfate corrosion, wet-dry cycles, and freeze-thaw damage. Chloride ions have difficulty reaching the surface of the reinforcing steel, significantly delaying steel corrosion; sulfate crystallization and expansion are less likely to cause cracking; and the lower water absorption rate weakens the destructive effects of freeze-thaw cycles. Ultimately, the service life of this concrete is significantly extended compared to traditional marine concrete.

[0026] In one embodiment, the cementitious material comprises the following components in parts by weight: 40-60 parts silicate cement, 20-30 parts ultrafine slag powder, 5-10 parts silica fume, 5-15 parts calcined metakaolin, and 5-10 parts fly ash microspheres.

[0027] The particle size of silicate cement is mainly in the micrometer range, while the particle size of ultrafine slag powder and fly ash microspheres is in the submicrometer to micrometer range. Silica fume particles are in the nanometer range, and calcined metakaolin particles are between nanometer and micrometer. The interfilling of particles of different sizes increases the bulk density of the cementitious material's solid particles, thereby significantly reducing the porosity and interconnected porosity of concrete.

[0028] Calcined metakaolin contains a large amount of active silica and alumina, which can react with calcium hydroxide produced during cement hydration to form products such as calcium aluminate hydrate. These products can chemically bind and solidify chloride ions in seawater. The solidified chloride ions are no longer free to move and cannot reach the surface of the reinforcing steel, thus directly delaying the corrosion process of the steel bars by chloride ions. Ultrafine slag powder and fly ash microspheres exert pozzolanic and micro-aggregate effects, significantly improving the density of concrete.

[0029] Furthermore, the combined use of multiple mineral admixtures effectively reduces the heat of hydration in the cementitious system. The hydration reaction of silicate cement releases a large amount of heat, especially in large-volume concrete structures, where the hydration temperature rise easily leads to temperature cracks. In this embodiment, the amount of silicate cement is controlled at 40-60 parts by weight, with the remainder consisting of mineral admixtures such as ultrafine slag powder, silica fume, calcined metakaolin, and fly ash microspheres. The heat of hydration of ultrafine slag powder is approximately 70%-80% of that of cement, while the heat of hydration of silica fume, metakaolin, and fly ash microspheres is even lower. Moreover, their pozzolanic reaction consumes some of the calcium hydroxide generated during cement hydration, resulting in a slower reaction rate and more gradual heat release. Therefore, with the same total amount of cementitious materials, the composite cementitious system in this embodiment has a lower peak hydration temperature rise and less cumulative heat release compared to pure cement or high-cement-content systems. This effectively suppresses early temperature shrinkage cracks caused by hydration temperature rise. Combined with the aforementioned fiber toughening and nano-reinforcement mechanisms, it further improves the crack resistance and long-term structural stability of concrete.

[0030] In one embodiment, the ultrafine slag powder has a specific surface area ≥800m² / kg, the silica fume has a SiO2 content ≥90% and a specific surface area ≥15000m² / kg, the calcined metakaolin has an activity index ≥110%, and the fly ash microspheres have a particle size ≤5μm.

[0031] In one embodiment, the nano-modified hydrophobic agent is a composite system formed by compounding silane nanoemulsion, calcium stearate and nano silica; based on the total mass of the composite system, the amount of nano silica is 5% to 10%, wherein the particle size of the nano silica is 20 to 50 nm.

[0032] Both silane nanoemulsion and calcium stearate are hydrophobic materials, and when combined, they are uniformly dispersed in concrete. After the concrete hardens, these hydrophobic components adhere to the inner walls of the capillary pores, forming a low-surface-energy hydrophobic layer that prevents water from wetting the pore walls. Water cannot penetrate, and the carriers of harmful substances such as chloride ions and sulfate ions that migrate with water are effectively blocked.

[0033] On the one hand, nano-silica with a particle size of 20–50 nm possesses extremely high specific surface area and surface activity. As a carrier, it can adsorb and stabilize the dispersion of silane emulsions and calcium stearate, preventing the agglomeration of hydrophobic components and ensuring their uniform distribution in concrete. On the other hand, nano-silica itself participates in the cement hydration reaction, reacting with calcium hydroxide to generate additional CSH gel, filling the pores and microcracks in the interfacial transition zone and improving the bond strength between cement paste and aggregate. Furthermore, the hydrophobic agent and the penetrating crystallizing material work synergistically to form a dual waterproofing mechanism of hydrophobicity and crystallization.

[0034] In one embodiment, the concentration of the graphene oxide dispersion is 5–10 mg / mL, the graphene oxide sheet diameter is 1–5 μm, and the carbon-to-oxygen ratio is 2.0–2.5. Graphene oxide possesses a high specific surface area and abundant oxygen-containing functional groups, which can act as a nanonucleating agent to promote the formation and orderly arrangement of hydration products, significantly improving the microstructure of cement paste. Simultaneously, graphene oxide can bridge microcracks, hinder crack propagation, and improve the crack resistance of concrete.

[0035] In one embodiment, the reinforcing fiber is basalt fiber or modified polypropylene fiber, with a length of 12-18 mm, a diameter of 15-25 μm, and an elastic modulus ≥40 GPa. The incorporation of basalt fiber or modified polypropylene fiber with a high elastic modulus effectively inhibits the formation of early-stage plastic shrinkage cracks and drying shrinkage cracks in concrete.

[0036] In one embodiment, the primary impermeability pressure of the internally incorporated cement-based permeable crystallizing material is ≥2.0 MPa, and the secondary impermeability pressure is ≥1.8 MPa.

[0037] Another aspect of this application provides a method for preparing high impermeability concrete in any of the above-mentioned marine environments, comprising the following steps: S1. Mix the graphene oxide dispersion, 50% of the total water volume, and polycarboxylate superplasticizer, and ultrasonically disperse for 5-10 minutes to obtain the graphene oxide pre-dispersion. S2. Dry mix the internally admixtured cement-based penetrating crystallizing material with the nano-modified water-repellent agent to obtain a functional component premix. S3. Silicate cement, ultrafine slag powder, silica fume, calcined metakaolin, and fly ash microspheres are mixed in proportion to obtain a composite cementitious material. S4. Add coarse aggregate, fine aggregate and reinforcing fiber to the mixer and dry mix for 30-60 seconds; S5. Add the composite cementitious material and functional component premix, and continue dry mixing for 30-60 seconds. S6. Add the remaining water and graphene oxide pre-dispersion liquid, and stir for 150-210s to obtain concrete mixture.

[0038] Step S1: The graphene oxide dispersion is first ultrasonically dispersed with 50% water to ensure thorough exfoliation and stable dispersion, preventing agglomeration during subsequent addition. Step S2: The internally adsorbed cement-based penetrating crystallizing material and the nano-modified water-repellent agent are dry-mixed evenly to ensure uniform distribution of the two functional components, facilitating subsequent synergistic effects. Steps S4 and S5: Aggregates and fibers are dry-mixed first, then the cementitious material and functional premix are added, ensuring uniform adhesion of fibers and powders to the aggregate surface and preventing fiber agglomeration. Step S6: The remaining water and graphene oxide predispersant are added, and the mixture is stirred to form a slurry that coats the aggregate. Finally, the graphene oxide predispersant is added to prevent premature contact with cement, which could lead to adsorption or flocculation, maintaining its good dispersion. Ultimately, all components are uniformly dispersed, avoiding agglomeration and localized enrichment, fully utilizing their respective functions, resulting in concrete with uniform and stable performance.

[0039] In one embodiment, the ultrasonic dispersion power in step S1 is 1.5–3 kW, and the frequency is 15–24 kHz. The preparation method of this application significantly improves the dispersion uniformity and stability of graphene oxide in concrete by employing industrial-grade high-power ultrasonic dispersion treatment at 2 kW and 20 kHz.

[0040] The high impermeability concrete provided in this application can be used for underground structures in marine engineering such as diaphragm walls, shear walls, pile foundations, and pile caps.

[0041] Examples and comparative examples: Example 1 Weigh the following raw materials per cubic meter: 240 kg of P.O42.5 silicate cement, 120 kg of ultrafine slag powder with a specific surface area of ​​850 m² / kg, 40 kg of silica fume, 60 kg of calcined metakaolin, and 40 kg of fly ash microspheres, totaling 500 kg of the above cementitious materials; 700 kg of medium-coarse river sand with a fineness modulus of 2.8; 1100 kg of 5-20 mm continuously graded crushed stone; 155 kg of water; 5 kg of polycarboxylate high-efficiency water-reducing agent with a water reduction rate of 32%; 13 kg of cement-based penetrating crystallizing material with internal admixture; 3 kg of nano-modified water-repellent agent composed of silane nanoemulsion and calcium stearate and containing 8% nano silica; 35 L of graphene oxide dispersion with a concentration of 10 mg / mL, of which the solid content of graphene oxide is 0.35 kg; and 2 kg of basalt fiber with a length of 15 mm.

[0042] After weighing, 35L of graphene oxide dispersion, 5kg of water-reducing agent, and 77.5kg of water were mixed and placed in a stainless steel container. The mixture was then treated with an ultrasonic disperser (20kHz, 2kW) for 8 minutes to obtain a pre-dispersed graphene oxide solution. 13kg of internally blended cementitious penetrating crystallizing material and 3kg of nano-modified water-repellent agent were added to a V-type mixer and stirred at 20rpm for 3 minutes to obtain a functional component premix. Separately, 240kg of P.O42.5 silicate cement, 120kg of ultrafine slag powder, 40kg of silica fume, 60kg of calcined metakaolin, and 40kg of fly ash microspheres were sequentially added to a twin-shaft forced mixer and dry-mixed at 35rpm for 2 minutes to obtain a composite cementitious material, which was then discharged for later use.

[0043] Subsequently, 1100 kg of coarse aggregate, 700 kg of fine aggregate, and 2 kg of basalt fiber were added to a twin-shaft forced mixer and dry-mixed at 35 rpm for 45 seconds to ensure the fiber was evenly adhered to the aggregate surface. Next, all the aforementioned composite cementitious materials and functional component premixes were added to the mixer and dry-mixed at 35 rpm for 45 seconds. Then, the remaining 77.5 kg of water was added to the mixer and mixed at 35 rpm for 75 seconds. Finally, all the graphene oxide pre-dispersion liquid was added to the mixer and mixed at 35 rpm for 105 seconds to obtain the concrete mixture. The mixture was placed into a 100 mm × 100 mm × 100 mm cubic mold, compacted on a vibrating table for 30 seconds, the surface was leveled, covered with plastic film, and left to stand at 20°C for 24 hours before demolding. The mixture was then transferred to a standard curing room at 20°C and relative humidity ≥95% for 28 days to obtain the high impermeability concrete for marine environments.

[0044] Example 2 Weigh the following raw materials per cubic meter: 260 kg of P.O42.5 silicate cement, 120 kg of ultrafine slag powder with a specific surface area of ​​850 m² / kg, 40 kg of silica fume, 40 kg of calcined metakaolin, and 20 kg of fly ash microspheres, totaling 480 kg of the above cementitious materials; 700 kg of medium-coarse river sand with a fineness modulus of 2.8; 1100 kg of 5-20 mm continuously graded crushed stone; 155 kg of water; 5 kg of polycarboxylate high-efficiency water-reducing agent with a water reduction rate of 32%; 12 kg of cement-based penetrating crystallizing material with internal admixture; 4 kg of nano-modified water-repellent agent composed of silane nanoemulsion and calcium stearate and containing 8% nano silica; 35 L of graphene oxide dispersion with a concentration of 10 mg / mL, of which the solid content of graphene oxide is 0.35 kg; and 2 kg of basalt fiber with a length of 15 mm.

[0045] After weighing, 35L of graphene oxide dispersion, 5kg of polycarboxylate superplasticizer, and 77.5kg of water were mixed and placed in a stainless steel container. The mixture was then treated with an ultrasonic disperser (20kHz, 2kW) for 8 minutes to obtain a pre-dispersed graphene oxide solution. 12kg of internally blended cementitious penetrating crystallizing material and 4kg of nano-modified water-repellent agent were added to a V-type mixer and stirred at 20rpm for 3 minutes to obtain a functional component premix. 260kg of cement, 120kg of ultrafine slag powder, 40kg of silica fume, 40kg of calcined metakaolin, and 20kg of fly ash microspheres were sequentially added to a twin-shaft forced mixer and dry-mixed at 35rpm for 2 minutes to obtain a composite cementitious material, which was then discharged for later use.

[0046] Subsequently, 1100 kg of coarse aggregate, 700 kg of fine aggregate, and 2 kg of basalt fiber were added to a twin-shaft forced mixer and dry-mixed at 35 rpm for 45 seconds to ensure the fiber was evenly adhered to the aggregate surface. Next, all the aforementioned composite cementitious materials and functional component premixes were added to the mixer and dry-mixed at 35 rpm for 45 seconds. Then, the remaining 77.5 kg of water was added to the mixer and mixed at 35 rpm for 75 seconds. Finally, all the graphene oxide pre-dispersion liquid was added to the mixer and mixed at 35 rpm for 105 seconds to obtain the concrete mixture. The mixture was placed into a 100 mm × 100 mm × 100 mm cubic mold, compacted on a vibrating table for 30 seconds, the surface was leveled, covered with plastic film, and left to stand at 20°C for 24 hours before demolding. The mixture was then transferred to a standard curing room at 20°C and relative humidity ≥95% for 28 days to obtain the high impermeability concrete for marine environments.

[0047] Example 3 Weigh the following raw materials per cubic meter: 240 kg of P.O42.5 silicate cement, 120 kg of ultrafine slag powder with a specific surface area of ​​850 m² / kg, 40 kg of silica fume, 60 kg of calcined metakaolin, and 40 kg of fly ash microspheres, totaling 500 kg of the above cementitious materials; 700 kg of medium-coarse river sand with a fineness modulus of 2.8; 1100 kg of 5-20 mm continuously graded crushed stone; 155 kg of water; 5 kg of polycarboxylate high-efficiency water-reducing agent with a water reduction rate of 32%; 13 kg of cement-based penetrating crystallizing material with internal admixture; 3 kg of nano-modified water-repellent agent composed of silane nanoemulsion and calcium stearate and containing 8% nano silica; 35 L of graphene oxide dispersion with a concentration of 10 mg / mL, of which the solid content of graphene oxide is 0.35 kg; and 2.5 kg of modified polypropylene fiber with a length of 12 mm.

[0048] After weighing, 35L of graphene oxide dispersion, 5kg of polycarboxylate superplasticizer, and 77.5kg of water were mixed and placed in a stainless steel container. The mixture was then treated with an ultrasonic disperser (20kHz, 2kW) for 8 minutes to obtain a pre-dispersed graphene oxide solution. 13kg of internally blended cement-based penetrating crystallizing material and 3kg of nano-modified water-repellent agent were added to a V-type mixer and stirred at 20rpm for 3 minutes to obtain a functional component premix. 240kg of cement, 120kg of ultrafine slag powder, 40kg of silica fume, 60kg of calcined metakaolin, and 40kg of fly ash microspheres were sequentially added to a twin-shaft forced mixer and dry-mixed at 35rpm for 2 minutes to obtain a composite cementitious material, which was then discharged for later use.

[0049] Subsequently, 1100 kg of coarse aggregate, 700 kg of fine aggregate, and 2.5 kg of modified polypropylene fiber were added to a twin-shaft forced mixer and dry-mixed at 35 rpm for 45 seconds to ensure the fiber was evenly adhered to the aggregate surface. Next, all the aforementioned composite cementitious materials and functional component premixes were added to the mixer and dry-mixed at 35 rpm for 45 seconds. Then, the remaining 77.5 kg of water was added to the mixer and mixed at 35 rpm for 75 seconds. Finally, all the graphene oxide pre-dispersion liquid was added to the mixer and mixed at 35 rpm for 105 seconds to obtain the concrete mixture. The mixture was placed into a 100 mm × 100 mm × 100 mm cubic mold, compacted on a vibrating table for 30 seconds, the surface was leveled, covered with plastic film, and left to stand at 20°C for 24 hours before demolding. The mixture was then transferred to a standard curing room at 20°C and relative humidity ≥95% for 28 days to obtain the high impermeability concrete for marine environments.

[0050] Comparative Example 1 Weigh the following raw materials per cubic meter: 420 kg of silicate cement; 80 kg of mineral powder; 680 kg of river sand; 1080 kg of crushed stone; 165 kg of water; and 6 kg of water-reducing agent. During preparation, add all raw materials to a mixer at once and mix thoroughly to obtain the concrete mixture. Shape the mixture, vibrate it, smooth the surface, and allow it to stand for 24 hours before removing the formwork. Allow it to cure for 28 days according to standard conditions.

[0051] Performance testing: According to the relevant standards, the mixture was molded into specimens of different sizes and types. Cubic specimens were used for testing compressive strength, chloride ion diffusion coefficient, electrical flux, and sulfate resistance coefficient; frustum specimens were used for testing impermeability grade and secondary impermeability pressure; prism specimens were used for drying shrinkage testing. The specimens were compacted on a vibrating table, the surface was smoothed, and covered with a plastic film. After standing at 20±2℃ for 24 hours, the molds were removed, and the specimens were moved to a standard curing room at 20±2℃ and relative humidity ≥95% for curing until the specified age. Performance tests were then conducted, yielding the following results: In Example 2, the changes were as follows: the amount of calcined metakaolin weighed was 40 kg, the amount of fly ash microspheres weighed was 20 kg, the amount of cement was adjusted to 260 kg, the amount of internally mixed cement-based penetrating crystallizing material was 12 kg, and the amount of nano-modified water-repellent agent was 4 kg.

[0052] In Example 3, the change was that the reinforcing fiber was replaced with modified polypropylene fiber (12 mm in length) instead of basalt fiber, with an admixture amount of 2.5 kg.

[0053] Test results show that the concrete prepared in each embodiment of the present invention is significantly superior to the comparative example in terms of compressive strength, impermeability, resistance to chloride ion penetration, resistance to sulfate attack, and volume stability. Among them, Example 1 has the best overall performance, with a 56-day compressive strength of 68.2 MPa and a secondary impermeability pressure of 2.15 MPa, indicating that it has excellent self-healing ability for microcracks.

[0054] The concrete prepared in the various embodiments of this invention exhibits ultra-high impermeability. Through optimization of the micro-gradation of cementitious materials, the densification effect of nanomaterials, and hydrophobic modification by water-repellent agents, the impermeability grade of the concrete can reach above P20 (Example 1 > P22), and the chloride ion diffusion coefficient is ≤2.11×10⁻⁶. -12 m 2 / s, with an electric flux ≤456 coulombs, and both the chloride ion diffusion coefficient and the electric flux decrease with optimization of the cementitious material composition.

[0055] Regarding self-healing capabilities, the internally incorporated cement-based penetrating crystalline material endows concrete with self-healing ability for microcracks. Example 1 showed a secondary seepage pressure of 2.15 MPa, indicating that the repaired cracks can still withstand high water pressure, significantly extending the service life of concrete structures in marine environments.

[0056] Furthermore, the concrete of this invention exhibits excellent volume stability. The multi-mineral admixtures reduce the heat of hydration, and the synergistic effect of nanomaterials and fibers in reinforcing crack resistance effectively controls drying shrinkage and thermal shrinkage. The 28-day drying shrinkage rate of Examples 1-3 is only (178-196) × 10⁻⁶. -8 This is far lower than the comparative example of 268×10 -8 The crack resistance is significantly improved.

[0057] Meanwhile, this invention balances environmental friendliness with excellent construction performance. The high-volume mineral admixtures replace a portion of the cement, reducing carbon emissions and aligning with the development direction of green building materials. The optimized particle size distribution and admixture system ensure good workability of the concrete, with minimal slump loss over time, making it suitable for pumping construction of structures such as underground shear walls.

[0058] It should be noted that the technical solutions or features described in the above embodiments can be combined or complemented each other without conflict. The scope of protection of this application is not limited to the precise structure described in the above embodiments; all modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A high-permeability concrete for marine environments, characterized in that, The components include the following parts by weight: 480-550 parts of cementitious material; 650-750 parts of fine aggregate; 1050-1150 parts coarse aggregate; 150-165 parts water; Polycarboxylate superplasticizer, 3.84–8.25 parts; 9.6–16.5 parts of internally adsorbed cement-based penetrating crystallizing material; 2-4 parts of nano-modified hydrophobic agent; 0.096–0.55 parts of graphene oxide dispersion; 1 to 3 parts of reinforcing fiber; wherein, the amount of components in the graphene oxide dispersion is measured according to the solid content of graphene oxide.

2. The high impermeability concrete for marine environments as described in claim 1, characterized in that, The cementitious material comprises the following components in parts by weight: 40-60 parts silicate cement, 20-30 parts ultrafine slag powder, 5-10 parts silica fume, 5-15 parts calcined metakaolin, and 5-10 parts fly ash microspheres.

3. The high impermeability concrete for marine environments as described in claim 2, characterized in that, The ultrafine slag powder has a specific surface area ≥800m² / kg, the silica fume has a SiO2 content ≥90% and a specific surface area ≥15000m² / kg, the calcined metakaolin has an activity index ≥110%, and the fly ash microspheres have a particle size ≤5μm.

4. The high impermeability concrete for marine environments as described in claim 1, characterized in that, The nano-modified hydrophobic agent is a composite system formed by combining silane nanoemulsion, calcium stearate and nano silica. Based on the total mass of the composite system, the doping amount of nano-silica is 5% to 10%, wherein the particle size of the nano-silica is 20 to 50 nm.

5. The high impermeability concrete for marine environments according to claim 1, characterized in that, The concentration of the graphene oxide dispersion is 5-10 mg / mL, the graphene oxide sheet diameter is 1-5 μm, and the carbon-to-oxygen ratio is 2.0-2.

5.

6. The high impermeability concrete for marine environments according to claim 1, characterized in that, The reinforcing fiber is basalt fiber or modified polypropylene fiber, with a length of 12-18 mm, a diameter of 15-25 μm, and an elastic modulus ≥40 GPa.

7. The high impermeability concrete for marine environments according to claim 1, characterized in that, The primary impermeability pressure of the internally incorporated cement-based permeable crystallizing material is ≥2.0 MPa, and the secondary impermeability pressure is ≥1.8 MPa.

8. A method for preparing high impermeability concrete in a marine environment as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Mix the graphene oxide dispersion, 50% of the total water volume with the polycarboxylate superplasticizer, and ultrasonically disperse for 5-10 minutes to obtain a graphene oxide predispersant. S2. The internally mixed cement-based penetrating crystallizing material and the nano-modified water-repellent agent are dry-mixed evenly to obtain a functional component premix. S3. The silicate cement, the ultrafine slag powder, the silica fume, the calcined metakaolin, and the fly ash microspheres are mixed in proportion to obtain a composite cementitious material. S4. Add the coarse aggregate, the fine aggregate and the reinforcing fiber into the mixer and dry mix for 30-60 seconds. S5. Add the composite cementitious material and the functional component premix, and continue dry mixing for 30-60 seconds. S6. Add the remaining water and the graphene oxide pre-dispersion liquid, and stir for 150-210 seconds to obtain the concrete mixture.

9. The preparation method according to claim 8, characterized in that, In step S1, the ultrasonic dispersion power is 1.5 to 3 kW and the frequency is 15 to 24 kHz.

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