Marine work pile foundation concrete with high chloride ion permeability resistance and preparation method of marine work pile foundation concrete

Abstract

The invention discloses maritime work pile foundation concrete with high chloride ion permeability resistance and a preparation method of the maritime work pile foundation concrete, and relates to the technical field of maritime work pile foundation materials.According to the concrete, a ZnAl-LDH-coated SiO core-shell structure composite nano modifier, alkali-activated fly ash-mineral powder-metakaolin composite admixture and silane-titanate compound modified aggregate are adopted to achieve a synergistic effect; the concrete is prepared through gradient mixing and stirring and an intelligent humidity feedback curing process in cooperation with a polycarboxylic acid type super-efficient water reducing agent and a composite air entraining agent. The problems that in the prior art, collaborative design is lacked, and it is difficult to consider high chloride ion permeability resistance, mechanical property and construction adaptability of marine pile foundation concrete at the same time are solved, concrete durability and engineering applicability are remarkably improved, and the method is suitable for pile foundation engineering in the harsh marine environment.

Description

Technical Field

[0001] This invention belongs to the technical field of marine engineering pile foundation concrete materials, specifically relating to a marine engineering pile foundation concrete with high resistance to chloride ion penetration and its preparation method. Background Technology

[0002] In the marine environment, marine engineering pile foundation concrete faces severe challenges such as high salt spray, high humidity, and chloride ion corrosion. Chloride ions can easily penetrate through the pores of concrete to the surface of the reinforcing steel, damaging the passivation film and causing corrosion, leading to decreased structural strength, shortened service life, and even structural safety hazards. Therefore, high resistance to chloride ion penetration has become a core performance requirement for marine engineering pile foundation concrete. As marine engineering develops towards deeper water and larger scale, the durability requirements for pile foundation concrete are constantly increasing. Especially in harsh environments such as long-term immersion and alternating wet and dry conditions, traditional concrete can no longer meet the industry's requirements for long-term design service life.

[0003] To improve resistance to chloride ion penetration, existing technologies often employ methods such as compounding with mineral admixtures, modification with nanomaterials, and addition of additives. While dual-blending systems of mineral admixtures, such as fly ash and mineral powder, can refine pores through a filling effect, they suffer from insufficient activation and slow early strength development. Nanomaterials, such as nano-SiO2 and layered double hydroxides, are prone to agglomeration when used alone, limiting their modification effect, and existing dispersion processes cannot completely solve this problem. Modifying aggregates with a single coupling agent can only improve interfacial bonding or water resistance, making it difficult to achieve a synergistic improvement in both properties. Curing processes often rely on timed watering or steam curing, which can easily lead to uneven humidity control, causing cracking on the concrete surface and reducing the effectiveness of the impermeability barrier.

[0004] Existing technologies primarily optimize for single performance defects, lacking synergistic design, making it difficult for concrete to simultaneously meet engineering requirements such as high chloride ion penetration resistance, high strength, and good construction compatibility. Therefore, developing a marine pile foundation concrete that systematically improves chloride ion penetration resistance through the synergistic effect of multiple components while also considering mechanical properties and engineering feasibility has become a pressing technical problem for the industry. Summary of the Invention

[0005] To overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a marine pile foundation concrete with high chloride ion permeability and its preparation method, which solves the problem in the prior art of lacking coordinated design and difficulty in simultaneously taking into account the high chloride ion permeability resistance, mechanical properties and construction adaptability of marine pile foundation concrete.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] A marine pile foundation concrete with high chloride ion penetration resistance is composed of the following components in parts by weight: 320-380 parts of P.II 52.5 silicate cement, 8-12 parts of ZnAl-LDH@SiO2 composite nano-modifier, 180-220 parts of alkali-activated fly ash-mineral powder-metakaolin composite admixture, 1250-1350 parts of silane-titanium ester composite modified aggregate, 3-5 parts of polycarboxylate-based ultra-high-efficiency water-reducing agent, 0.15-0.25 parts of composite air-entraining agent, and 150-170 parts of deionized water; wherein the ZnAl-LDH@SiO2 composite nano-modifier is a core-shell structured material of layered double hydroxide ZnAl-LDH loaded with nano-SiO2; the alkali-activated fly ash-mineral powder-metakaolin composite admixture is prepared using water glass-sodium hydroxide as a composite activator; and the total alkali content of the concrete is ≤3.0 kg / m³.

[0008] Furthermore, in the ZnAl-LDH@SiO2 composite nanomodifier, the mass ratio of ZnAl-LDH to nano-SiO2 is 1:3-1:5, and the molar ratio of Zn²⁺ to Al³⁺ is 2:1-3:1. The composite nanomodifier is prepared using a conventional in-situ growth process. During preparation, 2-3% by mass of γ-aminopropyltriethoxysilane is introduced for surface modification to improve the dispersion stability of the nanoparticles in the gelation system. The mass ratio of ZnAl-LDH to nano-SiO2 is limited to 1:3-1:5 because this ratio balances chloride ion adsorption capacity and pore barrier effect. If the ratio is too high, excessive nano-SiO2 will easily agglomerate; if it is too low, the chloride ion adsorption capacity will be insufficient, failing to fully utilize the synergistic advantages of the core-shell structure. The molar ratio of Zn²⁺ to Al³⁺ is limited to 2:1-3:1 because this range ensures the stability of the layered structure of the layered double hydroxides, guaranteeing the effectiveness of chloride ion exchange adsorption. Deviating from this range will cause the layered structure to collapse, resulting in loss of adsorption function. Introducing 2-3% (by mass) of γ-aminopropyltriethoxysilane for surface modification aims to address the agglomeration problem of nanoparticles in the gelation system, improve dispersion stability, prevent the modification effect from failing due to agglomeration, and ensure the uniformity of the core anti-permeability properties.

[0009] Furthermore, in the alkali-activated fly ash-mineral powder-metakaolin composite admixture, the mass ratio of fly ash, mineral powder, and metakaolin is 4:3:2; in the composite activator, the mass ratio of water glass to sodium hydroxide is 5:1-7:1, the modulus of water glass is 1.8-2.2, and the dosage of the composite activator is 8-12% of the total mass of the mixed mineral admixture. The mass ratio of fly ash, mineral powder, and metakaolin is limited to 4:3:2 to improve concrete density and ensure early strength development, avoiding performance shortcomings caused by single admixtures or improper proportions. The mass ratio of water glass to sodium hydroxide in the composite activator is limited to 5:1-7:1, and the modulus of water glass is limited to 1.8-2.2 because this ratio and modulus allow for precise control of the hydration reaction rate, ensuring sufficient activation of the three admixtures. A modulus that is too high or too low will reduce activation efficiency, and an imbalanced ratio will lead to unstable hydration products. The dosage of the composite activator is limited to 8-12% of the total mass of the mixed mineral admixtures in order to balance the activation effect and cost. If the dosage is too low, the activation effect cannot be fully activated, while if it is too high, it will lead to increased concrete shrinkage, causing cracking risk and affecting the impermeability.

[0010] Furthermore, in the silane-titanium ester composite modified aggregate, the mass ratio of silane coupling agent to titanate coupling agent is 2:1, the silane coupling agent is KH-560, and the titanate coupling agent is NDZ-311; the coarse aggregate is 5-25mm continuously graded diabase crushed stone, and the fine aggregate is clean river sand with a fineness modulus of 2.7-2.9, with a mass ratio of coarse aggregate to fine aggregate of 3.2:1-3.4:1; the total amount of coupling agent composite is 0.3-0.4% of the aggregate mass. The mass ratio of silane coupling agent to titanate coupling agent is limited to 2:1 because this ratio can synergistically exert the chemical bonding effect of silane coupling agent and the hydrophobic modification effect of titanate coupling agent, thereby improving the interfacial bonding strength and enhancing the water resistance of the aggregate surface, avoiding the functional limitations of single coupling agent modification. The silane coupling agent KH560 and the titanate coupling agent NDZ311 were specifically chosen because these two coupling agents exhibit good compatibility with concrete systems, stable modification effects, and can meet the durability requirements of harsh marine environments. The coarse aggregate was specified as 5-25mm continuously graded diabase crushed stone, and the fine aggregate as clean river sand with a fineness modulus of 2.7-2.9, with a coarse aggregate to fine aggregate mass ratio of 3.2:1-3.4:1. This aggregate type offers high strength and good wear resistance; continuous gradation and a reasonable sand ratio ensure concrete density, reduce porosity, and improve the impermeability of the foundation. The total treatment amount of the coupling agent compound was limited to 0.3-0.4% of the aggregate mass to ensure modification effectiveness while controlling costs. Too low a treatment amount would fail to form an effective modified layer, while too high an amount would lead to a decline in the performance of the interfacial transition zone.

[0011] Furthermore, the polycarboxylate-based ultra-high-efficiency water-reducing agent has a water reduction rate of ≥38%, a solid content of 45-50%, and is chloride-free; the composite air-entraining agent is a compound of sodium rosinate and sodium fatty alcohol polyoxyethylene ether sulfate, with a mass ratio of 4:1. The reason for limiting the polycarboxylate-based ultra-high-efficiency water-reducing agent to a water reduction rate of ≥38%, a solid content of 45-50%, and chloride-free is that a high water reduction rate ensures good fluidity of concrete under low water-cement ratio conditions, meeting the construction requirements of layered pouring for marine pile foundations; a suitable solid content ensures stable water reduction effect; and the absence of chloride prevents the introduction of chloride ions that could cause steel corrosion, meeting the core corrosion resistance requirements of marine concrete. The composite air-entraining agent is specified as a mixture of sodium rosinate and sodium fatty alcohol polyoxyethylene ether sulfate in a mass ratio of 4:1 because these two components have good compatibility and can form uniform and stable microbubbles. This refines the internal pores of concrete, reduces chloride ion penetration channels, and improves the frost resistance of concrete. This ratio can balance the number and pore size of bubbles, avoiding the problem of too many bubbles affecting strength or too few bubbles failing to exert the anti-permeability and anti-frost effect.

[0012] The high chloride ion permeability resistance marine pile foundation concrete of this invention achieves a synergistic effect of chloride ion adsorption and pore barrier by using a ZnAl-LDH@SiO2 core-shell structure composite nano-modifier. Alkali-activated fly ash, mineral powder, and metakaolin composite admixture enhance the synergistic activity of mineral components and the densification of hydration products. Silane titanate composite modified aggregate improves the interfacial adhesion between aggregate and cementitious system and enhances water permeability resistance. Polycarboxylate-based ultra-high-efficiency water-reducing agent and composite air-entraining agent ensure concrete workability. A gradient mixing process ensures uniform dispersion of all components. Intelligent humidity feedback curing maintains stable humidity throughout the curing process. This multi-component, multi-process synergistic technical solution avoids the risks of alkali-aggregate reaction and steel corrosion while comprehensively improving the chloride ion permeability resistance, mechanical properties, and construction adaptability of marine pile foundation concrete, meeting the long-term durability requirements of harsh marine environments.

[0013] As a general inventive concept, this invention provides a method for preparing marine pile foundation concrete with high chloride ion permeability as described above, comprising the following steps:

[0014] S1. Raw material pretreatment: Prepare alkali-activated fly ash-mineral powder-metakaolin composite admixture, dry it and pass it through an 80-mesh sieve for later use; Modify coarse and fine aggregates with silane-titanium ester composite to obtain silane-titanium ester composite modified aggregate; Disperse ZnAl-LDH@SiO2 composite nano-modifier in an ultrasonic disperser for 12-18 min with ultrasonic power of 350-450W, then mix it with polycarboxylate-based ultra-high-efficiency water-reducing agent and composite air-entraining agent, add 35-40% of deionized water, and stir at 350-400 r / min for 18-22 min to obtain a stable premix;

[0015] S2. Gradient mixing: P・Ⅱ52.5 silicate cement and alkali-activated fly ash-mineral powder-meta-kaolin composite admixture are added to a twin-shaft forced mixer and dry-mixed at 450-500 r / min for 1.5-2 min until there is no obvious color difference or lumps; silane-titanium ester composite modified aggregate is added, and the speed is adjusted to 350-400 r / min and mixed for 2.5-3 min; stabilized premix liquid is slowly added, and the speed is maintained for 1 min before adding the remaining deionized water, and the speed is increased to 500-550 r / min and mixed for 3.5-4.5 min to obtain concrete mixture;

[0016] S3. Casting and shaping: The concrete mixture is poured into the pre-set pile foundation template and compacted by layering with an immersion high-frequency vibrator. The vibration frequency is 60-70Hz, the spacing between vibration points is 350-400mm, the thickness of each layer is ≤500mm, and each vibration point is vibrated for 25-30s.

[0017] S4. Intelligent humidity feedback curing: Steam curing is initiated within 8-12 hours after pouring, with a heating rate of 5-6℃ / h. The curing temperature is controlled at 45-50℃, and the relative humidity is ≥92%. After 48 hours of constant temperature curing, the temperature is reduced to ambient temperature at a rate of ≤8℃ / h. After steam curing, the entire surface is wrapped with geotextile and humidity sensors are installed for intelligent water spraying curing, maintaining the relative humidity of the curing environment at ≥95%. The curing time is 28 days. During the curing period, humidity data is monitored in real time, and the water spraying system is automatically activated to replenish water when the humidity is lower than the set value.

[0018] Further, the specific conditions for the silane-titanium ester compound modification in step S1 are as follows: the silane coupling agent and the titanate coupling agent are diluted with anhydrous ethanol to a mass concentration of 6-7%, and uniformly sprayed onto the surface of aggregate dried to constant weight. After stirring and mixing for 15-20 minutes, the mixture is dried at a constant temperature of 60-65℃ for 3-4 hours and then cooled to room temperature for later use. The coupling agent compound is diluted with anhydrous ethanol to a mass concentration of 6-7% because this concentration ensures both sufficient dissolution of the coupling agent and uniform coverage of the aggregate surface. Too high a concentration can lead to agglomeration of the coupling agent, preventing the formation of a continuous modified layer; too low a concentration will fail to achieve complete modification of the aggregate surface. The purpose of uniformly spraying the coupling agent onto the surface of the aggregate dried to constant weight and stirring and mixing for 15-20 minutes is to ensure sufficient contact between the coupling agent and the aggregate surface, guaranteeing a complete modification reaction. The limitation of drying at a constant temperature of 60-65℃ for 3-4 hours is to promote the chemical bonding reaction between the coupling agent and the aggregate surface, while removing residual ethanol and water to avoid the residual water affecting the setting and hardening of concrete. Cooling to room temperature for later use can prevent high-temperature aggregate from affecting the subsequent hydration reaction of cementitious materials and ensure the stability of modified aggregate performance.

[0019] Furthermore, in step S2, the workability of the concrete mixture is monitored in real time during the mixing process, controlling the slump to 170-190mm and the spread to 450-500mm. The initial setting time, measured using the inverted cone method, is 12-14 hours. This initial setting time is suitable for the construction time window of layered pouring and vibration of marine pile foundations, ensuring interlayer bond strength and construction continuity. The slump of 170-190mm and the spread of 450-500mm are controlled here because the workability within this range meets the construction requirements of layered pouring of marine pile foundations, ensuring good fluidity and spreadability of the concrete for easy filling of all corners of the formwork, while avoiding excessive fluidity that could lead to aggregate segregation. Limiting the initial setting time to 12-14 hours and specifying the construction window that this time is suitable for is to balance the continuity of construction and the integrity of the structure. This ensures that the lower layer of concrete has not yet set during layered pouring, thus ensuring the interlayer bond strength, while also avoiding the impact of excessively long initial setting time on the efficiency of subsequent processes. This solves the problem of poor interlayer bonding or construction delays caused by the mismatch between the initial setting time and the construction rhythm in existing technologies.

[0020] Furthermore, in step S3, the insertion depth of the immersion-type high-frequency vibrator is 1.8-2.0 times the maximum aggregate size, inserted 50-80mm into the lower layer of poured concrete. After vibrating until the concrete surface is uniformly covered with slurry and no obvious air bubbles rise to the surface, it is slowly withdrawn to avoid structural defects caused by insufficient or excessive vibration. The specific insertion depth of 1.8-2.0 times the maximum aggregate size and 50-80mm into the lower layer of concrete ensures full fusion between the upper and lower layers of concrete, preventing interlayer gaps. Slowly withdrawing the vibrator after uniformly covering the surface with slurry and no obvious air bubbles prevents rapid withdrawal from creating negative pressure that introduces new air bubbles, while also avoiding over-vibration that could lead to aggregate segregation, thus ensuring a uniform and dense internal structure of the concrete.

[0021] Furthermore, during the intelligent water spraying curing process in step S4, the ambient temperature is maintained between 18-32℃. When the ambient temperature is below 18℃, an insulation layer is added to the outside of the curing layer to ensure that the curing environment temperature does not fall below 18℃. When the ambient temperature is above 32℃, the water spraying frequency is increased to once every 2 hours to prevent the curing layer from losing water too quickly and causing surface cracks. The curing environment temperature is limited to 18-32℃ because this temperature range ensures that the concrete hydration reaction proceeds smoothly. Too low a temperature will significantly slow down the hydration process and affect strength development, while too high a temperature will cause the hydration reaction to be too fast, which can easily generate internal stress and cause cracks. Adding an insulation layer when the ambient temperature is below 18℃ is to maintain the curing environment temperature and prevent the concrete surface temperature from dropping suddenly and causing temperature cracks. Increasing the water spraying frequency to once every 2 hours when the ambient temperature is above 32℃ is to replenish water in time and prevent the curing layer from losing water too quickly, which would lead to surface drying, shrinkage, and cracking, thus providing good conditions for the development of concrete strength and the formation of impermeability.

[0022] The present invention provides a method for preparing marine pile foundation concrete with high chloride ion permeability resistance. This method addresses the core problems of uneven mixing leading to component synergistic failure and passive curing methods causing imbalances in humidity and temperature control. The goal is to ensure the full utilization of the synergistic advantages of multiple components and to construct a stable anti-permeability barrier. It eliminates impurities and agglomeration risks through raw material pretreatment, employs a gradient mixing process to achieve uniform dispersion and efficient fusion of components, and combines this with an intelligent humidity feedback curing process to precisely control the temperature and humidity environment throughout the curing process. This forms a comprehensive "pretreatment-mixing-curing" synergistic control system, avoiding structural defects caused by improper mixing and suppressing temperature cracks and early dehydration cracks. This ensures a stable improvement in concrete density and chloride ion permeability resistance, while also meeting the construction requirements of marine pile foundation projects.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] (1) This invention constructs a multi-dimensional anti-permeability barrier through the adsorption-blocking synergy of core-shell structure composite nano-modifier, the densification effect of composite admixture and the interface strengthening of modified aggregate, effectively delaying the corrosion of steel bars caused by chloride ion erosion and extending the service life of marine pile foundation structure.

[0025] (2) The active synergistic effect of the alkali-activated admixture of the present invention improves the density and strength of concrete, the gradient mixing process ensures uniform dispersion of components, and the reasonable initial setting time design and vibration parameters ensure strong interlayer bonding and avoid structural defects.

[0026] (3) The high water-reducing admixture of the present invention and its reasonable working performance indicators are adapted to the layered pouring requirements of marine pile foundations. No new special equipment is required, and the existing construction system can be directly applied, reducing construction difficulty and cost.

[0027] (4) The low alkali content design of this invention avoids the risk of alkali-aggregate reaction, the composite air-entraining agent optimizes the internal pore structure, and the intelligent temperature and humidity curing inhibits the generation of cracks, making the concrete resistant to harsh environments such as high salt spray in the ocean and alternating wet and dry conditions.

[0028] (5) This invention utilizes industrial waste such as fly ash to prepare composite admixtures, reducing cement usage and carbon emissions. Furthermore, the components and process parameters are adapted to industrial production, taking into account both technological innovation and industrial promotion value. Attached Figure Description

[0029] Figure 1 This is a flowchart of a marine pile foundation concrete with high chloride ion permeability and its preparation method according to the present invention. Detailed Implementation

[0030] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1

[0034] A high chloride ion penetration resistance marine pile foundation concrete of the present invention is composed of the following components in parts by weight: 350 parts of P.II 52.5 silicate cement, 10 parts of ZnAl-LDH@SiO2 composite nano-modifier, 200 parts of alkali-activated fly ash-mineral powder-metakaolin composite admixture, 1300 parts of silane-titanium ester composite modified aggregate, 4 parts of polycarboxylate-based ultra-high efficiency water-reducing agent, 0.2 parts of composite air-entraining agent, and 160 parts of deionized water; ZnAl-LDH@SiO2... The composite nano-modifier is a core-shell structured material of layered double hydroxide ZnAl-LDH supporting nano-SiO2, wherein the mass ratio of ZnAl-LDH to nano-SiO2 is 1:4, and the molar ratio of Zn²⁺ to Al³⁺ is 2.5:1. The composite nano-modifier is prepared based on conventional in-situ growth processes in the field, and 2.5% by mass of γ-aminopropyltriethoxysilane is introduced for surface modification during the preparation process; alkali-activated fly ash-mineral powder-metakaolin composite admixture is used... Water glass-sodium hydroxide composite activator is prepared, wherein the mass ratio of fly ash, mineral powder, and metakaolin is 4:3:2, the mass ratio of water glass to sodium hydroxide in the composite activator is 6:1, the modulus of water glass is 2.0, and the dosage of the composite activator is 10% of the total mass of the mixed mineral admixtures; in silane-titanium ester composite modified aggregate, the mass ratio of silane coupling agent to titanate coupling agent is 2:1, the silane coupling agent is KH560, the titanate coupling agent is NDZ311, and the coarse aggregate... The concrete is composed of diabase crushed stone with a continuous gradation of 5-25mm, fine aggregate is clean river sand with a fineness modulus of 2.8, coarse aggregate to fine aggregate mass ratio is 3.3:1, and the total treatment amount of the coupling agent compound is 0.35% of the aggregate mass; the water reduction rate of the polycarboxylate-based ultra-high efficiency water-reducing agent is ≥38%, the solid content is 48%, and it is chloride-free; the composite air-entraining agent is a compound of sodium rosinate and sodium fatty alcohol polyoxyethylene ether sulfate, with a mass ratio of 4:1; the total alkali content of the concrete is ≤3.0kg / m³.

[0035] refer to Figure 1The method for preparing marine pile foundation concrete with high chloride ion permeability according to this embodiment includes the following steps:

[0036] S1. Raw material pretreatment: Prepare alkali-activated fly ash-mineral powder-metakaolin composite admixture, dry and pass through an 80-mesh sieve for later use; Modify coarse and fine aggregates with silane-titanium ester composites: Dilute silane coupling agent and titanate coupling agent with anhydrous ethanol to a mass concentration of 6.5%, spray evenly on the surface of aggregates dried to constant weight, stir and mix for 18 min, dry at 62℃ for 3.5 h, and cool to room temperature to obtain silane-titanium ester composite modified aggregates; Disperse ZnAl-LDH@SiO2 composite nano-modifier in an ultrasonic disperser for 15 min with an ultrasonic power of 400 W, then mix with polycarboxylate-based ultra-high-efficiency water-reducing agent and composite air-entraining agent, add 38% deionized water, stir at 370 r / min for 20 min to obtain a stable premix;

[0037] S2. Gradient mixing: P・Ⅱ52.5 silicate cement and alkali-activated fly ash-mineral powder-meta-kaolin composite admixture were added to a twin-shaft forced mixer and dry-mixed at 480 r / min for 1.8 min until there was no obvious color difference or lumps; silane-titanium ester composite modified aggregate was added, and the speed was adjusted to 370 r / min and mixed for 2.8 min; stabilized premix liquid was slowly added, and the speed was maintained for 1 min before adding the remaining deionized water, and the speed was increased to 520 r / min and mixed for 4 min to obtain concrete mixture. The workability of concrete mixture was monitored in real time during the mixing process, and the slump was controlled at 180 mm, the spread at 480 mm, and the initial setting time measured by the inverted cone method was 13 h.

[0038] S3. Casting and shaping: The concrete mixture is poured into the pre-set pile foundation template and compacted by layering with an immersion high-frequency vibrator. The vibration frequency is 65Hz, the vibration point spacing is 370mm, the thickness of each layer is ≤500mm, and each vibration point is vibrated for 28s. The insertion depth of the immersion high-frequency vibrator is 1.9 times the maximum particle size of the aggregate. It is inserted 65mm into the lower layer of poured concrete. After vibration until the concrete surface is uniformly covered with slurry and no obvious air bubbles rise to the surface, it is slowly pulled out.

[0039] S4. Intelligent humidity feedback curing: Steam curing is initiated within 10 hours after pouring, with a heating rate of 5.2℃ / h. The curing temperature is controlled at 48℃, and the relative humidity is ≥92%. After 48 hours of constant temperature curing, the temperature is reduced to ambient temperature at a rate of 7℃ / h. After steam curing, the entire surface is wrapped with geotextile and humidity sensors are installed for intelligent water spraying curing, maintaining the relative humidity of the curing environment at ≥95%. The curing time is 28 days. During the curing period, humidity data is monitored in real time. When the humidity is lower than the set value, the water spraying system is automatically activated to replenish water. During intelligent water spraying curing, the ambient temperature is maintained at 25℃.

[0040] Example 2

[0041] The difference between this embodiment and Example 1 is that the mass ratio of ZnAl-LDH to nano-SiO2 in the ZnAl-LDH@SiO2 composite nano-modifier is 1:3.5, while the other components, preparation methods and parameters are completely consistent with Example 1.

[0042] Example 3

[0043] The difference between this embodiment and Embodiment 1 is that the amount of composite activator in the alkali-activated composite admixture is 9% of the total mass of the mixed mineral admixture, while the remaining components, preparation methods and parameters are completely consistent with Embodiment 1.

[0044] Example 4

[0045] The difference between this embodiment and Example 1 is that the total amount of coupling agent compound in the silane-titanium ester compound modified aggregate is 0.32% of the aggregate mass, while the remaining components, preparation methods and parameters are completely consistent with Example 1.

[0046] Example 5

[0047] The difference between this embodiment and Embodiment 1 is that the stirring speed after adding aggregate in the gradient mixing step is 380 r / min, while the other components, preparation methods and parameters are completely consistent with Embodiment 1.

[0048] Example 6

[0049] The difference between this embodiment and Embodiment 1 is that the heating rate of steam curing in the intelligent humidity feedback curing step is 5.5℃ / h, while the other components, preparation methods and parameters are completely consistent with Embodiment 1.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the ZnAl-LDH@SiO2 composite nanomodifier is removed and replaced with 10 parts of single nano-SiO2. This single nano-SiO2 is not loaded with ZnAl-LDH and has not been modified with γ-aminopropyltriethoxysilane. The remaining components, preparation methods and parameters are completely consistent with those of Example 1.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 1 is that the alkali-activated fly ash-mineral powder-meta-kaolin composite admixture is removed and replaced with 200 parts of fly ash-mineral powder dual admixture. The mass ratio of fly ash to mineral powder in this dual admixture is 4:3. No meta-kaolin is added and there is no composite activator. The remaining components, preparation methods and parameters are completely consistent with those of Example 1.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that the silane-titanium ester composite modified aggregate is replaced with a single KH560 modified aggregate. The amount of single KH560 is the same as the total amount of the silane-titanium ester coupling agent composite in Example 1. NDZ311 is not added. All other components, preparation methods and parameters are completely consistent with Example 1.

[0056] Comparative Example 4

[0057] The difference between this comparative example and Example 1 is that the gradient mixing and stirring is replaced by conventional single-speed stirring. The stirring process is to add all raw materials at a speed of 400 r / min throughout the process and stir for 8 minutes. The remaining components, preparation methods and parameters are completely consistent with Example 1.

[0058] Comparative Example 5

[0059] The difference between this comparative example and Example 1 is that the intelligent humidity feedback curing is replaced by conventional timed water spraying curing. Specifically, after the steam curing is completed, water is sprayed 3 times a day. No humidity sensor is installed and there is no automatic water replenishment function. The other components, preparation methods and parameters are completely consistent with Example 1.

[0060] Comparative Example 6

[0061] The difference between this comparative example and Example 1 is that the polycarboxylate-based ultra-high-efficiency water-reducing agent is replaced with a chloride-containing water-reducing agent. The water-reducing rate of this chloride-containing water-reducing agent is 38%, the solid content is 48%, and the chloride content is 0.5% by mass. The remaining components, preparation methods, and parameters are completely consistent with those of Example 1.

[0062] The testing method is as follows:

[0063] 1. Chloride ion diffusion coefficient: The chloride ion diffusion coefficient of concrete at 28 days of age was determined according to the "Standard for Test Methods of Long-term Performance and Durability of Concrete" (GB / T50082-2009).

[0064] 2.28d compressive strength: According to the "Standard for Test Methods of Mechanical Properties of Concrete" (GB / T50081-2019), 150mm×150mm×150mm cubic specimens were prepared and the compressive strength was tested after standard curing for 28 days.

[0065] 3. Interlayer bond strength: Refer to the "Standard for Test Methods of Concrete Structures" (GB / T50152-2012) and use the double-sided shear test method to determine the interlayer bond strength of layered concrete.

[0066] 4. Freeze-thaw resistance grade: According to the "Standard for Test Methods of Long-term Performance and Durability of Concrete" (GB / T50082-2009), the rapid freezing method is adopted, and the concrete mass loss rate is ≤5% and the relative dynamic modulus of elasticity is ≥60% as the control indicators to determine the freeze-thaw resistance grade;

[0067] 5. Corrosion rate of steel bars after 2000h salt spray corrosion: A 2000h neutral salt spray corrosion test was conducted according to the "Artificial Atmosphere Corrosion Test - Salt Spray Test" (GB / T10125-2021). The mass change of steel bars before and after corrosion was determined by the weight loss method, and the corrosion rate was calculated.

[0068] Table 1: Experimental Results of Examples 1-6 and Comparative Examples 1-6

[0069] Case Chloride ion diffusion coefficient (10⁻¹²m² / s) 28-day compressive strength (MPa) Interlayer bond strength (MPa) Freeze resistance rating Rust rate of reinforcing steel after 2000 hours of salt spray corrosion (%) Example 1 2.1 58.6 4.2 F300 0.35 Example 2 2.3 57.8 4.1 F300 0.38 Example 3 2.4 56.5 4.0 F250 0.42 Example 4 2.2 57.2 3.9 F250 0.39 Example 5 2.3 58.1 4.3 F300 0.37 Example 6 2.2 58.3 4.2 F300 0.36 Comparative Example 1 5.8 52.3 3.8 F200 1.28 Comparative Example 2 6.2 53.0 3.5 F150 1.45 Comparative Example 3 5.5 53.1 3.2 F200 1.16 Comparative Example 4 4.9 51.8 3.0 F200 0.98 Comparative Example 5 4.7 52.5 3.4 F100 1.05 Comparative Example 6 2.5 56.3 4.0 F250 2.83

[0070] In summary, referring to Table 1, the chloride ion diffusion coefficient, 28-day compressive strength, interlayer bond strength, freeze-thaw resistance grade, and steel corrosion rate of the embodiment are significantly better than those of the comparative example, demonstrating the technical advantages of the present invention in multi-component synergy and full-process process control.

[0071] Comparative Example 1, lacking the adsorption-barrier synergistic effect of the ZnAl-LDH@SiO2 composite nano-modifier, showed that single nano-SiO2 could not effectively block chloride ion penetration, leading to a significant increase in the chloride ion diffusion coefficient and an increase in steel corrosion rate. Comparative Example 2, using dual-admixture mineral admixtures without a composite activator, lacked the active synergistic effect of the three-admixture system, resulting in insufficient concrete density and a simultaneous decline in mechanical and impermeability properties. Comparative Example 3, using a single coupling agent to modify aggregate, failed to achieve a synergistic improvement in interfacial bonding and water resistance, resulting in thin interlayer bond strength. The concrete was weak, and chloride ions could easily penetrate through the interfacial gaps. Comparative Example 4 used conventional single-speed mixing, resulting in uneven mixing of the components, defects in the internal structure of the concrete, and a deterioration in mechanical properties and impermeability stability. Comparative Example 5 used conventional timed watering for curing, but it was impossible to accurately control the curing humidity, which made the concrete surface prone to cracks, increased pore connectivity, and significantly reduced the freeze-thaw resistance and durability. Comparative Example 6 used a chloride-containing water-reducing agent, and chloride ions directly caused steel corrosion. Although the impermeability and mechanical properties were less affected, the steel corrosion rate increased dramatically, posing a serious threat to long-term durability.

[0072] Example 1: Due to the synergistic effect of the core-shell modifier composite admixture modified aggregate and the whole-process control of gradient mixing and intelligent curing, the optimal performance indicators were achieved.

[0073] Example 2 shows that due to the suitable mass ratio of ZnAl-LDH to nano-SiO2, the adsorption-barrier synergistic effect of the core-shell structure is stable, and the impermeability and durability are well maintained.

[0074] In Example 3, the composite activator dosage was reasonable, although slightly lower than the benchmark value, it could still effectively activate the activity of the three-mineral admixture, ensuring that the mechanical properties and impermeability met the standards.

[0075] Example 4 shows that the amount of coupling agent compound is suitable for the surface modification requirements of aggregates, the interfacial bonding force is stable, and there is no significant fluctuation in various performance indicators.

[0076] In Example 5, due to the reasonable stirring speed of the aggregate during gradient mixing, the components were uniformly dispersed, resulting in a slight improvement in interlayer bond strength and mechanical properties.

[0077] Example 6 shows that the steam curing heating rate is adapted to the concrete hydration process, effectively inhibiting the generation of temperature cracks and ensuring stable impermeability and durability.

Claims

1. A marine pile foundation concrete with high resistance to chloride ion penetration, characterized in that: The concrete is composed of the following components in parts by weight: 320-380 parts of P-II 52.5 silicate cement, 8-12 parts of ZnAl-LDH@SiO2 composite nano-modifier, 180-220 parts of alkali-activated fly ash-mineral powder-metakaolin composite admixture, 1250-1350 parts of silane-titanium ester composite modified aggregate, 3-5 parts of polycarboxylate-based ultra-high-efficiency water-reducing agent, 0.15-0.25 parts of composite air-entraining agent, and 150-170 parts of deionized water. The ZnAl-LDH@SiO2 composite nano-modifier is a core-shell structured material of layered double hydroxide ZnAl-LDH supporting nano-SiO2. The alkali-activated fly ash-mineral powder-metakaolin composite admixture is prepared using water glass-sodium hydroxide as a composite activator. The total alkali content of the concrete is ≤3.0 kg / m³.

2. The marine pile foundation concrete according to claim 1, characterized in that: In the ZnAl-LDH@SiO2 composite nanomodifier, the mass ratio of ZnAl-LDH to nano SiO2 is 1:3-1:5, and the molar ratio of Zn²⁺ to Al³⁺ is 2:1-3:

1. The composite nanomodifier is prepared based on conventional in-situ growth processes in the art. During the preparation process, 2-3% by mass of γ-aminopropyltriethoxysilane is introduced for surface modification to improve the dispersion stability of nanoparticles in the gelation system.

3. The marine pile foundation concrete according to claim 1, characterized in that: In the alkali-activated fly ash-mineral powder-metakaolin composite admixture, the mass ratio of fly ash, mineral powder, and metakaolin is 4:3:2; in the composite activator, the mass ratio of water glass to sodium hydroxide is 5:1-7:1, the modulus of water glass is 1.8-2.2, and the dosage of the composite activator is 8-12% of the total mass of the mixed mineral admixture.

4. The marine pile foundation concrete according to claim 1, characterized in that: In the silane-titanium ester composite modified aggregate, the mass ratio of silane coupling agent to titanate coupling agent is 2:1, the silane coupling agent is KH-560, and the titanate coupling agent is NDZ-311; the coarse aggregate is 5-25mm continuously graded diabase crushed stone, the fine aggregate is clean river sand with a fineness modulus of 2.7-2.9, and the mass ratio of coarse aggregate to fine aggregate is 3.2:1-3.4:1; the total amount of coupling agent composite is 0.3-0.4% of the aggregate mass.

5. The marine pile foundation concrete according to claim 1, characterized in that: The polycarboxylate-based ultra-high-efficiency water-reducing agent has a water reduction rate of ≥38%, a solid content of 45-50%, and is free of chloride salts; the composite air-entraining agent is a compound of sodium rosinate and sodium fatty alcohol polyoxyethylene ether sulfate, with a mass ratio of 4:

1.

6. A method for preparing marine pile foundation concrete with high resistance to chloride ion penetration, characterized in that: Includes the following steps, S1. Raw material pretreatment: Prepare alkali-activated fly ash-mineral powder-metakaolin composite admixture, dry it and pass it through an 80-mesh sieve for later use; Modify coarse and fine aggregates with silane-titanium ester composite to obtain silane-titanium ester composite modified aggregate; Disperse ZnAl-LDH@SiO2 composite nano-modifier in an ultrasonic disperser for 12-18 min with ultrasonic power of 350-450W, then mix it with polycarboxylate-based ultra-high-efficiency water-reducing agent and composite air-entraining agent, add 35-40% of deionized water, and stir at 350-400 r / min for 18-22 min to obtain a stable premix; S2. Gradient mixing: P・Ⅱ52.5 silicate cement and alkali-activated fly ash-mineral powder-meta-kaolin composite admixture are added to a twin-shaft forced mixer and dry-mixed at 450-500 r / min for 1.5-2 min until there is no obvious color difference or lumps; silane-titanium ester composite modified aggregate is added, and the speed is adjusted to 350-400 r / min and mixed for 2.5-3 min; stabilized premix liquid is slowly added, and the speed is maintained for 1 min before adding the remaining deionized water, and the speed is increased to 500-550 r / min and mixed for 3.5-4.5 min to obtain concrete mixture; S3. Casting and shaping: The concrete mixture is poured into the pre-set pile foundation template and compacted by layering with an immersion high-frequency vibrator. The vibration frequency is 60-70Hz, the spacing between vibration points is 350-400mm, the thickness of each layer is ≤500mm, and each vibration point is vibrated for 25-30s. S4. Intelligent humidity feedback curing: Steam curing is initiated within 8-12 hours after pouring, with a heating rate of 5-6℃ / h. The curing temperature is controlled at 45-50℃, and the relative humidity is ≥92%. After 48 hours of constant temperature curing, the temperature is reduced to ambient temperature at a rate of ≤8℃ / h. After steam curing, the entire surface is wrapped with geotextile and humidity sensors are installed for intelligent water spraying curing, maintaining the relative humidity of the curing environment at ≥95%. The curing time is 28 days. During the curing period, humidity data is monitored in real time, and the water spraying system is automatically activated to replenish water when the humidity is lower than the set value.

7. The method for preparing marine pile foundation concrete with high chloride ion permeability according to claim 6, characterized in that: The specific conditions for the silane-titanium ester compound modification in step S1 are as follows: dilute the silane coupling agent and the titanate coupling agent with anhydrous ethanol to a mass concentration of 6-7%, spray them evenly on the surface of the aggregate dried to constant weight, stir and mix for 15-20 minutes, dry at a constant temperature of 60-65℃ for 3-4 hours, and cool to room temperature for later use.

8. The method for preparing marine pile foundation concrete with high chloride ion permeability according to claim 6, characterized in that: In step S2, the workability of the concrete mixture is monitored in real time during the mixing process, and the slump is controlled to be 170-190mm and the spread to be 450-500mm. The initial setting time measured by the inverted cone method is 12-14h. This initial setting time is suitable for the construction time window of layered pouring and vibration of marine pile foundation, ensuring the interlayer bond strength and construction continuity.

9. The method for preparing marine pile foundation concrete with high chloride ion permeability according to claim 6, characterized in that: In step S3, the insertion depth of the immersion-type high-frequency vibrator is 1.8-2.0 times the maximum particle size of the aggregate. It is inserted 50-80mm into the lower layer of poured concrete. After vibrating until the concrete surface is uniformly covered with slurry and no obvious air bubbles rise to the surface, it is slowly pulled out to avoid structural defects caused by insufficient or excessive vibration.

10. The method for preparing marine pile foundation concrete with high chloride ion permeability according to claim 6, characterized in that: During the intelligent water spraying maintenance in step S4, the ambient temperature is maintained between 18-32℃. When the ambient temperature is below 18℃, an insulation cotton layer is added to the outside of the maintenance layer to ensure that the maintenance ambient temperature is not lower than 18℃. When the ambient temperature is above 32℃, the water spraying frequency is increased to once every 2 hours to avoid the maintenance layer losing water too quickly and causing surface cracks.

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