Corrosion-resistant concrete for shield tunnel segment and preparation method of corrosion-resistant concrete

Abstract

The invention belongs to the technical field of concrete materials, and particularly relates to corrosion-resistant concrete for shield tunnel segments and a preparation method of the corrosion-resistant concrete. The concrete comprises sulphoaluminate cement, fly ash, slag powder, machine-made sand, gravel, a polycarboxylate superplasticizer, a defoaming agent, water and two key modified components, wherein the two key modified components comprise a layered double hydroxide-aluminum silicate nanosheet compound and a phosphate radical intercalation modified strontium molybdate slow-release corrosion inhibitor. During preparation, firstly, all the dry materials are put into a stirrer for dry mixing, then water and the additive are added for stirring to obtain mixed slurry, and a finished product is obtained after pouring, vibrating and steam curing. Wherein the two modified compounds are synthesized through a specific process, the former can adsorb corrosive ions and refine pores, and the latter can slowly release corrosion-inhibiting ions to protect reinforcing steel bars. The prepared concrete has excellent chloride ion penetration resistance, sulfate erosion resistance and carbonization resistance, the durability is remarkably improved, and the concrete is particularly suitable for shield tunnel segments in the severe corrosion environment.

Description

Technical Field

[0001] This invention belongs to the field of concrete materials technology, specifically relating to a corrosion-resistant concrete for shield tunnel segments and its preparation method. Background Technology

[0002] As a key structural form for modern urban underground transportation, water conservancy projects, and cross-sea passages, the long-term safety and durability of shield tunnels heavily rely on the precast concrete segments that make up the tunnel ring. These segments operate in complex and harsh underground or underwater environments throughout their service life, facing the combined threat of corrosion from multiple factors, including groundwater, soil, and stray currents. Among these, chloride ion penetration-induced internal steel reinforcement corrosion, sulfate erosion-induced concrete expansion and pulverization, and high carbon dioxide concentrations within the relatively enclosed tunnel space leading to concrete carbonization are recognized as the three main pathological mechanisms causing performance degradation and shortened structural lifespan of shield tunnel segments. Especially in coastal areas or strata containing corrosive ions, traditional segment concrete often struggles to effectively resist the long-term intrusion of these corrosive agents, leading to a chain reaction of problems such as protective layer spalling, steel reinforcement cross-sectional loss, reduced load-bearing capacity, and even leakage. This not only results in high maintenance and repair costs but also poses a potential risk to the operational safety of underground engineering projects. Therefore, developing a special concrete material with ultra-high corrosion resistance to ensure the integrity and functionality of shield tunnel structures within the design reference period has become an urgent and practically significant issue in the field of civil engineering materials.

[0003] Currently, the main technical approaches to improving the durability of concrete in shield tunnel segments focus on two aspects: optimizing the concrete's own density and introducing external protective measures. Regarding material optimization, a low water-cement ratio design is commonly adopted, along with the incorporation of mineral admixtures such as fly ash and slag powder, aiming to refine the pore structure and reduce permeability through the pozzolanic effect. Simultaneously, adding various admixtures during the concrete mixing stage has become an important method, such as incorporating inorganic crystalline waterproofing materials to block capillary channels, or using migration-type corrosion inhibitors to form a protective film on the steel reinforcement surface. For external protection, the application of organic coatings such as epoxy resin and polyurethane to the outer curved surface of the segments is commonly used as an additional physical barrier. However, these existing technical solutions still have significant limitations. While mineral admixtures have a positive effect on improving the matrix's impermeability, their ability to subsequently adsorb and fix already penetrated corrosive ions, especially chloride ions, is limited, and their resistance to combined sulfate and chloride ion corrosion is not ideal. Traditional rust inhibitors may suffer from problems such as easy migration of active ingredients, rapid consumption, poor compatibility with concrete systems, or insufficient environmental friendliness, raising doubts about the reliability of their long-term protective effects. Surface coatings, on the other hand, have drawbacks such as difficulty in controlling construction quality, susceptibility to damage during transportation and installation, and inherent durability issues due to aging; damage may even accelerate localized corrosion. Therefore, there is an urgent need to develop a fundamental solution that can proactively, sustainably, and synergistically resist multiple corrosive agents from within the concrete.

[0004] To address the aforementioned technical bottlenecks, the core idea of ​​this invention lies in breaking through the limitations of traditional methods that rely solely on increasing density or simply adding single-function admixtures. Instead, it shifts towards designing and introducing novel compounds with specific microstructures and intelligent response functions, constructing a built-in dual-protection system from two fundamental dimensions: "strengthening the matrix" and "actively protecting the reinforcing steel." This invention aims to provide a novel corrosion-resistant concrete for shield tunnel segments. Its key lies in the original preparation and application of two functionally complementary inorganic modifying compounds: one designed to construct a "molecular trap" capable of strongly adsorbing and locking harmful anions such as chloride and sulfate ions, while simultaneously optimizing the microstructure of cement paste; the other designed as an "ion storage device" that can stably exist in the pore liquid environment of concrete and intelligently release highly efficient rust-inhibiting components according to environmental changes, achieving long-lasting electrochemical protection for the reinforcing steel. These two compounds, through scientific compounding with sulfate-resistant cement, selected mineral admixtures and high-efficiency water-reducing agents, are expected to form a comprehensive defense system that penetrates the concrete body and has both physical barrier and chemical passivation functions without sacrificing the workability and early strength of concrete. This will provide a revolutionary material basis for shield tunnel segments to cope with extreme corrosive environments and meet the stringent requirements of major projects for 100-year durability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a corrosion-resistant concrete for shield tunnel segments and its preparation method.

[0006] In a first aspect, the present invention provides a method for preparing corrosion-resistant concrete for shield tunnel segments, comprising the following steps: S1. By weight, add 350-380 parts of sulfoaluminate cement, 50-70 parts of fly ash, 80-100 parts of slag powder, 8-12 parts of layered bimetallic hydroxide-alumina silicate nanosheet composite, 5-8 parts of phosphate intercalated modified strontium molybdate slow-release rust inhibitor, 720-750 parts of manufactured sand, 450-480 parts of 5-10mm crushed stone, and 680-720 parts of 10-20mm crushed stone to a mixer and dry mix. S2. Add 130-145 parts water, 4.8-6.5 parts polycarboxylate superplasticizer and 0.3-0.6 parts defoamer to the mixer and stir to obtain a mixed slurry. Pour the mixed slurry into the mold and vibrate it. After the initial setting of the slurry, move the mold to the steam curing kiln. After the heating stage reaches 50-60℃, maintain the temperature and cure it at a constant temperature, and then cool it down to room temperature.

[0007] In this invention, the preparation reaction mechanism of corrosion-resistant concrete for shield tunnel segments is essentially a physical mixing and chemical synergistic process of multi-component, multi-scale materials under specific processes, aiming to construct a complete protective system from micro to macro, from matrix to reinforcement. Driven by mechanical stirring, the dry components (including sulfoaluminate cement, mineral admixtures, two functional compounds, and aggregates at various levels) first achieve uniform dispersion at the macro scale, forming a tightly packed dry mix skeleton. Subsequently, the addition of mixing water triggers a complex hydration and physicochemical reaction network. Cement clinker minerals rapidly hydrate, generating products such as hydrated calcium silicate gel and ettringite, forming the strength foundation of the concrete; fly ash and slag powder undergo a pozzolanic reaction, consuming the calcium hydroxide produced by hydration and generating additional low-alkalinity hydrated calcium silicate gel. This process significantly refines the slurry pores and improves the density of the matrix. In this process, the two functional compounds deeply participate and play a key role. Layered bimetallic hydroxide-aluminum silicate nanosheet composites, leveraging their nanoscale effect, act as ultrafine fillers, directly filling the micro- and nanopores between cement hydration products, physically reducing porosity and torturing capillary channels. Simultaneously, their layered structure enables ion exchange and adsorption, pre-capturing small amounts of harmful substances such as free chloride ions introduced from raw materials or present in the environment during the initial hydration stage. Meanwhile, phosphate-intercalated modified strontium molybdate slow-release corrosion inhibitors are dispersed in the slurry, their surface contacting cement hydration products. Their stable internal intercalation structure ensures only trace amounts of corrosion-inhibiting ions are released in the highly alkaline environment during the initial hardening of concrete. These ions diffuse to the surface of the reinforcing steel, participating in the formation of an initial dense passivation film. Polycarboxylate superplasticizer molecules effectively disperse cement particles and release encapsulated water through steric hindrance and electrostatic repulsion, imparting excellent workability to fresh concrete. Defoamers eliminate harmful large air bubbles introduced during mixing, further improving the density and homogeneity of the hardened concrete. After pouring, vibration compaction, and steam curing, this multiphase composite system further solidifies, the hydration reaction accelerates and approaches completion, and functional compounds are firmly embedded in the hardened cementitious matrix. The resulting concrete has a highly dense and functionally integrated microstructure: the cementitious matrix itself has small pores due to the low water-cement ratio and mineral admixtures; the nanosheet composite acts as a microscopic "sentinel" to adsorb and fix corrosive ions; and the corrosion inhibitor acts as an "ion reservoir" next to the reinforcing steel, providing long-term protection. This synergistic effect of multiple mechanisms gives the concrete excellent comprehensive durability against chloride ion penetration, sulfate attack, and carbonation.

[0008] According to a preferred embodiment of the present invention, in step S1, the dry mixing time is 30-60 seconds.

[0009] According to a preferred embodiment of the present invention, in step S2, the constant temperature curing time is 2-4 hours.

[0010] According to a preferred embodiment of the present invention, the preparation method of the layered bimetallic hydroxide-aluminum silicate nanosheet composite includes: A1, dissolving 10-14 parts by weight of magnesium nitrate hexahydrate and 4-8 parts by weight of aluminum nitrate nonahydrate in 180-220 parts by weight of deionized water to obtain a mixed salt solution A; dissolving 5-6 parts by weight of sodium hydroxide and 4-5 parts by weight of anhydrous sodium carbonate in 90-110 parts by weight of deionized water to obtain a mixed alkaline solution B; and adding the mixed alkaline solution B to the mixed salt solution under nitrogen protection and continuous stirring. In liquid A, adjust the pH to 9.8-10.2, and crystallize and age at 64-66℃. Collect the slurry by centrifugation, and wash the slurry with deionized water until neutral to obtain a wet filter cake. A2, redisperse the wet filter cake in 140-160 parts of an aqueous solution containing 2-4 parts of sodium silicate and 0.4-0.6 parts of hexadecyltrimethylammonium bromide. In a high-pressure reactor, perform a hydrothermal reaction at 118-122℃ to obtain the product. Centrifuge, wash, and vacuum dry the product at 78-82℃, grind, and sieve.

[0011] In this invention, the preparation mechanism of the layered bimetallic hydroxide-aluminum silicate nanosheet composite involves a complex process of ion co-precipitation, crystallization growth, in-situ hydrolysis guided by surfactants, and self-assembly. This process begins with the co-precipitation of magnesium and aluminum salts in an alkaline environment. Magnesium and aluminum ions in the solution, under the influence of hydroxide ions, together with simultaneously introduced carbonate ions, construct a magnesium-aluminum carbonate-type hydrotalcite precursor with a regular layered structure. The layers of this precursor are composed of magnesium-oxygen octahedra and aluminum-oxygen octahedra connected by shared edges and carry a positive charge. Carbonate ions, acting as anions to balance the charge, are embedded in the interlayer domains. Its formation requires strict pH control and isothermal crystallization conditions to ensure crystallinity and layer regularity. After obtaining this precursor, the key step is to carry out a hydrothermal reaction with sodium silicate in the presence of a surfactant. During this stage, surfactant molecules adsorb onto the surface of the precursor layers, and through steric hindrance and electrostatic interactions, cause limited exfoliation of the layers, producing partially independent nanosheets. Meanwhile, sodium silicate undergoes hydrolysis and condensation under high temperature and pressure hydrothermal conditions. The resulting silicate species further combine with aluminum species in the system to form amorphous aluminosilicate oligomers or nanoparticles. These newly formed aluminosilicate species, under the templating action of surfactants, strongly interact with the exfoliated layered bimetallic hydroxide nanosheets, potentially reassembling through chemical bonding or physical entanglement into a stable composite structure where a layered inorganic framework and amorphous aluminosilicate nanosheets support and interweave each other. This final product inherits the strong anion intercalation and trapping ability of layered bimetallic hydroxides, while the introduction of aluminosilicate nanosheets enhances structural stability and dispersibility, and provides additional nanofilling effects.

[0012] According to a preferred embodiment of the present invention, in step A1, the crystallization aging time at 64-66°C is 18-20 hours.

[0013] According to a preferred embodiment of the present invention, in step A2, the hydrothermal reaction time at 118-122°C is 12-14 hours.

[0014] According to a preferred embodiment of the present invention, the preparation method of the phosphate intercalation modified strontium molybdate slow-release rust inhibitor includes: B1, dissolving 6-10 parts by weight of ammonium heptamolybdate and 4-6 parts by weight of strontium chloride in hot water at 78-82°C to obtain a mixture; transferring the mixture to a high-pressure reactor, reacting at 140-160°C, naturally cooling, filtering, obtaining a washing solution, washing the precipitate with deionized water to obtain the precursor strontium molybdate; grinding and mixing the precursor strontium molybdate with 14-16 parts by weight of diammonium hydrogen phosphate and 1-3 parts by weight of urea to obtain a mixture; B2, placing the mixture in a muffle furnace, calcining at 495-505°C in an air atmosphere; naturally cooling after calcination to obtain a block product, crushing and grinding the block product.

[0015] In this invention, the preparation of the phosphate-intercalated modified strontium molybdate slow-release rust inhibitor follows a step-by-step strategy of first constructing a crystalline framework and then performing intercalation modification via a high-temperature solid-state reaction. The first step involves the hydrothermal synthesis of a strontium molybdate precursor. Ammonium molybdate and strontium salt undergo a metathesis reaction in water under heating conditions to generate strontium molybdate precipitate. The high-temperature hydrothermal environment promotes the growth of this precipitate crystals, resulting in a basic compound with a specific grain size and morphology. The second step, calcination modification, is the core innovation of this preparation method. Its mechanism involves solid-state ion diffusion and intercalation chemical reactions at high temperatures. The strontium molybdate precursor is uniformly mixed with diammonium hydrogen phosphate and urea, and then calcined in air with a programmed temperature increase. Urea decomposes during heating, producing a reducing atmosphere such as ammonia, which affects the local microenvironment. Diammonium hydrogen phosphate decomposes upon heating, releasing ammonia, water, and active phosphorus species, such as phosphate and pyrophosphate. Under specific medium-temperature calcination conditions, these active phosphorus species do not simply adhere to the surface of strontium molybdate crystals. Instead, due to their small ionic radius and high reactivity, some enter the interlayer channels or specific interplanar gaps of the strontium molybdate lattice through thermal diffusion. Simultaneously, the reducing atmosphere generated during decomposition may induce valence changes or local structural adjustments in some molybdate ions, thereby forming defect sites within the crystal suitable for the "intercalation" or "bonding" of phosphate ions. Ultimately, some phosphate ions exist stably within the strontium molybdate lattice in an intercalated form, forming a composite crystal structure with unique slow-release properties. This structure ensures that rust-inhibiting ions (molybdate and phosphate) can be released slowly and controllably in the alkaline environment of concrete pore fluid, achieving long-term protection.

[0016] According to a preferred embodiment of the present invention, in step B1, the reaction time at 140-160°C is 6-8 hours.

[0017] According to a preferred embodiment of the present invention, in step B2, the calcination time at 495-505°C is 3-5 hours.

[0018] In a second aspect, the present invention provides a corrosion-resistant concrete for shield tunnel segments prepared according to the method described above.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The corrosion-resistant concrete for shield tunnel segments provided by this invention, through the original introduction of layered bimetallic hydroxide-alumina silicate nanosheet composite and phosphate-intercalated modified strontium molybdate slow-release rust inhibitor, and scientific compounding with optimized sulfoaluminate cementitious cementitious system and fine-graded aggregate, ultimately achieves a qualitative leap in the durability of concrete materials under extreme corrosive environments. Its core effect lies in constructing a multi-level synergistic protection system from macro to micro, from physical barrier to chemical intelligent response. This system first significantly improves the ability of concrete to resist the intrusion of corrosive media from the material's inherent nature. As one of the core components, the layered bimetallic hydroxide-alumina silicate nanosheet composite plays a dual role as a "molecular adsorption trap" and a "microstructure optimizer". Its unique layered structure exhibits strong selective adsorption and interlayer fixation capabilities for chloride and sulfate ions, effectively capturing free harmful ions that penetrate the concrete interior and locking them between the layers. This significantly slows down or even prevents their migration to the steel reinforcement surface, fundamentally cutting off the key pathways that induce steel corrosion. Simultaneously, the aluminum silicate nanosheets in this composite are uniformly dispersed in the cement paste, exhibiting excellent micro-aggregate filling effects. This further refines the pore structure of the cement paste, reduces total porosity, and optimizes pore size distribution, significantly enhancing the physical density and impermeability of the concrete matrix, establishing a solid first line of defense against the diffusion of various corrosive media.

[0020] (2) Based on the strengthening of the concrete matrix, this invention further provides active, long-lasting, and intelligent protection for the internal steel reinforcement by modifying the strontium molybdate slow-release corrosion inhibitor with phosphate intercalation, forming a unique second electrochemical protective barrier. This corrosion inhibitor does not simply release corrosion-inhibiting components in a traditional manner, but rather stores effective molybdate and phosphate corrosion-inhibiting ions in the lattice channels through a carefully designed intercalated crystal structure. In the normal alkaline environment of concrete, its release rate is extremely slow, ensuring long-term effectiveness; once the local environment experiences a decrease in micro-area alkalinity due to the intrusion of carbonization or corrosive ions, this structure can intelligently respond and moderately accelerate the release of corrosion-inhibiting ions. These released molybdate and phosphate ions can preferentially adsorb onto the surface of the steel reinforcement before harmful substances such as chloride ions, participating in and strengthening the formation and repair of the steel reinforcement passivation film, forming a denser and more stable protective layer, thereby significantly improving the corrosion initiation threshold and pitting resistance of the steel reinforcement. This "on-demand" slow-release mechanism not only greatly improves rust-inhibiting efficiency and avoids the problems of early rapid consumption or late failure of traditional rust inhibitors, but also works synergistically with the aforementioned base protective layer to ensure the high safety of the reinforcing steel throughout its entire design service life.

[0021] (3) The technical solution of this invention also brings about a comprehensive improvement in overall performance and good engineering applicability. First, the introduction of the two functional compounds not only does not impair the workability and mechanical properties of concrete, but also makes a positive contribution. The nanosheet structure of the layered composite helps to improve the rheological properties of the slurry. In synergy with the polycarboxylate superplasticizer, the concrete can still obtain excellent fluidity and cohesiveness at a low water-cement ratio, effectively solving the problems of high construction difficulty and easy bleeding and segregation that are often associated with high-strength and high-durability concrete, and ensuring the dense filling of the complex mold cavity and excellent appearance quality during the prefabrication of the segments. At the same time, the optimization effect of these nanomaterials on the microstructure of cement hydration products also directly contributes to the steady increase of early and late strength of concrete. Second, all components in the entire system, including the two core modified compounds, are inorganic materials, which are environmentally friendly and do not have the disadvantages of aging, migration or volatilization of organic matter. Their durability is comparable to that of the concrete itself, ensuring the long-term stability of the protective effect for a century. Finally, the concrete preparation method is fully compatible with the standard process flow of existing industrialized shield tunnel segment production, from dry mixing and wet mixing to steam curing, requiring no major modifications to existing production lines, thus facilitating large-scale promotion and application. In summary, this invention successfully prepares a special concrete for shield tunnel segments that combines ultra-high corrosion resistance, excellent workability, stable mechanical strength, and outstanding long-term durability, providing a reliable and advanced material solution for major underground engineering construction in harsh corrosive environments. Detailed Implementation

[0022] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0023] Example 1

[0024] This embodiment provides a method for preparing corrosion-resistant concrete for shield tunnel segments, the steps of which include: Preparation of layered bimetallic hydroxide-aluminum silicate nanosheet composite: First, 12.00 g of magnesium nitrate hexahydrate and 6.00 g of aluminum nitrate nonahydrate were weighed and completely dissolved in 200.00 mL of degassed deionized water to form a clear mixed salt solution A under magnetic stirring. Then, 5.30 g of sodium hydroxide and 4.20 g of anhydrous sodium carbonate were weighed and dissolved in 100.00 mL of deionized water to form a mixed alkaline solution B. Under a nitrogen atmosphere to eliminate carbon dioxide, the mixed alkaline solution B was slowly added dropwise to the vigorously stirred mixed salt solution A through a constant-pressure dropping funnel at a rate of 1 to 2 drops per second. During the addition, a pH meter was used to monitor the pH in real time, and the pH of the entire reaction system was precisely adjusted and maintained at 10.0 by adding a small amount of dilute sodium hydroxide solution. After the addition was complete, the mixed reaction solution was transferred to a constant-temperature water bath shaker and crystallized and aged at 65.0 °C and a rotation speed of 150 rpm for 18.0 hours. After the reaction, the slurry was collected by centrifuging at 8000 rpm for 10 minutes using a high-speed centrifuge. The supernatant was discarded, and the precipitate was redispersed with deionized water and centrifuged again. This washing process was repeated 5 times until the pH of the supernatant after centrifugation was neutral, finally yielding a wet filter cake. Next, the obtained wet filter cake was transferred to a beaker, and a solution prepared by dissolving 3.00 g of sodium silicate and 0.50 g of hexadecyltrimethylammonium bromide in 150.00 mL of deionized water was added. The solution was dispersed under ultrasonic assistance for 30 minutes to form a homogeneous suspension. This suspension was transferred to a 200 mL polytetrafluoroethylene-lined high-pressure reactor, sealed, and placed in an oven. The temperature was increased to 120.0 °C at a rate of 2 °C / min, and maintained at this temperature for a hydrothermal reaction for 12.0 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The product was then removed from the reactor, separated by centrifugation again, and washed three times each with anhydrous ethanol and deionized water. The washed solid was placed in a vacuum drying oven and dried at 80.0℃ for 24.0 hours. Finally, the dried block was ground in an agate mortar and passed through a 200-mesh standard sieve to obtain a layered bimetallic hydroxide-aluminum silicate nanosheet composite, which was then placed in a desiccator for later use.

[0025] Preparation of phosphate-intercalated modified strontium molybdate slow-release rust inhibitor: Weigh 8.00 g ammonium heptamolybdate and 5.00 g strontium chloride hexahydrate, and dissolve them separately in 50 mL of deionized water preheated to 80.0 °C. After complete dissolution, rapidly mix the two solutions in a beaker with stirring, immediately forming a white precipitate. Pour the mixed suspension into a polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in an oven. Increase the temperature to 150.0 °C at 3 °C / min and maintain the temperature for 6.0 hours. After the reaction, allow it to cool naturally to below 60 °C in the oven, then remove it and perform vacuum filtration using a Buchner funnel and slow-speed quantitative filter paper. Collect the solid precipitate and wash it repeatedly with hot deionized water at 80 °C until the filtrate is free of chloride ions when tested with silver nitrate solution. Dry the washed precipitate in an oven at 100.0 °C for 6 hours to obtain the precursor strontium molybdate. Accurately weigh 15.00g of the dried precursor strontium molybdate, 14.00g of diammonium hydrogen phosphate, and 2.00g of urea. Place them in an agate mortar and grind by hand for 45 minutes until the material is a uniform grayish-white color. Transfer the uniformly mixed powder to a corundum crucible and place it in a box-type muffle furnace. Under air atmosphere, heat the furnace from room temperature to 500.0℃ at a rate of 5℃ / min, and calcine at this temperature for 3.0 hours. After calcination, turn off the power and allow the muffle furnace to cool naturally to room temperature. Remove the crucible, gently crush the slightly agglomerated product after sintering, and grind it again in the mortar for 30 minutes. Pass the powder through a 400-mesh sieve to obtain phosphate-intercalated modified strontium molybdate slow-release rust inhibitor powder, and store it in a sealed container.

[0026] Preparation of corrosion-resistant concrete for shield tunnel segments: Accurately weigh the following raw materials according to their mass: 365.0g sulfoaluminate cement, 60.0g Grade I fly ash, 90.0g S95 grade slag powder, 10.0g of the aforementioned layered bimetallic hydroxide-alumina silicate nanosheet composite, 6.5g of the aforementioned phosphate-intercalated modified strontium molybdate slow-release rust inhibitor, 735.0g of manufactured sand with a fineness modulus of 2.8, 465.0g of crushed stone with a particle size of 5-10mm, and 700.0g of crushed stone with a particle size of 10-20mm. Add all the above solid raw materials at once to a 50L forced-type single-shaft concrete mixer. Start the mixer and dry mix at a speed of 45±5rpm for 45 seconds to ensure that the powder and aggregate are initially and evenly mixed. Subsequently, the pre-mixed liquid components, consisting of 138.0g tap water, 5.20g polycarboxylate superplasticizer with a solid content of 40%, and 0.45g silicone defoamer, are poured into the mixer at a uniform speed within 10 seconds. The mixer speed is increased to 60±5 rpm, and wet mixing is carried out for 120 seconds until the mixture exhibits a uniform gray color, consistent surface gloss, and no visible bleeding or segregation, thus obtaining the fresh concrete slurry. This slurry is immediately poured into standard-sized shield tunnel segment steel molds, using a Φ50mm immersion vibrator, with a grid-like distribution, vibrating at each point for 15-18 seconds, until the concrete surface is covered with slurry and air bubbles are mostly expelled. After pouring, the concrete is left to stand in a curing room at a temperature of 20±2℃ and a relative humidity greater than 95% until initial setting. Afterward, the molds, along with the tunnel segments, are transported via rail to a steam curing kiln, and the kiln door is closed. Initiate the curing procedure: Increase the temperature inside the kiln uniformly to 55.0℃ within 90 minutes at a heating rate of 15℃ / h, and maintain this temperature for 3.0 hours. After the temperature maintenance period, slowly decrease the temperature at a rate of 10℃ / h, reducing the kiln temperature to less than 20℃ below the ambient temperature within 180 minutes. Then, open the kiln door to complete the curing process. Finally, demold the concrete segment specimens.

[0027] Example 2

[0028] The difference between this embodiment and Example 1 lies in the preparation of the layered bimetallic hydroxide-aluminum silicate nanosheet composite: 10.00 g of magnesium nitrate hexahydrate and 8.00 g of aluminum nitrate nonahydrate were dissolved in 190.0 mL of deionized water to obtain solution A; 5.00 g of sodium hydroxide and 5.00 g of anhydrous sodium carbonate were dissolved in 105.0 mL of deionized water to obtain solution B. Under nitrogen protection, solution B was added dropwise to solution A while it was being stirred, the pH was adjusted to 9.9, and the mixture was crystallized and aged at 64.0 °C for 19.0 hours. Subsequent centrifugation and washing operations were the same as in Example 1. The resulting wet filter cake was dispersed in 155.0 mL of an aqueous solution containing 2.00 g of sodium silicate and 0.60 g of hexadecyltrimethylammonium bromide, ultrasonically dispersed, and then transferred to an autoclave for hydrothermal reaction at 118.0 °C for 13.0 hours. Subsequent centrifugation, washing, drying, grinding, and sieving steps were the same as in Example 1 to obtain the layered bimetallic hydroxide-aluminum silicate nanosheet composite.

[0029] Preparation of phosphate-intercalated modified strontium molybdate slow-release rust inhibitor: 6.00 g of ammonium heptamolybdate and 6.00 g of strontium chloride hexahydrate were dissolved in hot water at 80 °C. After mixing, the mixture was transferred to an autoclave and reacted at 145.0 °C for 7.0 hours. After reaction, the mixture was cooled, filtered, and the precipitate was washed with hot water until no chloride ions were found. The precipitate was then dried to obtain the precursor. 16.00 g of the precursor was weighed and ground together with 16.00 g of diammonium hydrogen phosphate and 1.00 g of urea for 40 minutes. The mixture was placed in a muffle furnace and calcined at 498.0 °C for 4.0 hours using the same procedure. After cooling in the furnace, the mixture was ground through a 400-mesh sieve to obtain the phosphate-intercalated modified strontium molybdate slow-release rust inhibitor.

[0030] Preparation of corrosion-resistant concrete for shield tunnel segments: Accurately weigh the following raw materials: 370.0g sulfoaluminate cement, 55.0g Grade I fly ash, 95.0g Grade S95 slag powder, 9.0g of the aforementioned composite material, 7.0g of the aforementioned rust inhibitor, 740.0g manufactured sand, 470.0g 5-10mm crushed stone, and 690.0g 10-20mm crushed stone. Add all solid raw materials to a mixer and dry mix at 45±5 rpm for 50 seconds. Add a mixture consisting of 142.0g tap water, 5.80g polycarboxylate superplasticizer, and 0.50g defoamer, and wet mix at 60±5 rpm for 110 seconds to obtain a uniform slurry. The pouring and vibration processes are the same as in Example 1. After initial setting, steam curing is performed: the temperature is increased to 58.0℃ at a rate of 18℃ / h, and the temperature is maintained for 2.5 hours. Then, the temperature is reduced to the required temperature difference at a rate of 12℃ / h before demolding.

[0031] Example 3

[0032] The difference between this embodiment and Example 1 lies in the preparation of the layered bimetallic hydroxide-aluminum silicate nanosheet composite: 14.00 g of magnesium nitrate hexahydrate and 4.00 g of aluminum nitrate nonahydrate were dissolved in 210.0 mL of deionized water to obtain solution A; 6.00 g of sodium hydroxide and 4.50 g of anhydrous sodium carbonate were dissolved in 95.0 mL of deionized water to obtain solution B. Under nitrogen protection, solution B was added dropwise to solution A while it was being stirred, the pH was adjusted to 10.1, and the mixture was crystallized and aged at 66.0 °C for 20.0 hours. Subsequent centrifugation and washing operations were the same as in Example 1. The resulting wet filter cake was dispersed in 145.0 mL of an aqueous solution containing 4.00 g of sodium silicate and 0.40 g of hexadecyltrimethylammonium bromide, ultrasonically dispersed, and then transferred to an autoclave for hydrothermal reaction at 122.0 °C for 14.0 hours. Subsequent centrifugation, washing, drying, grinding, and sieving steps were the same as in Example 1 to obtain the layered bimetallic hydroxide-aluminum silicate nanosheet composite.

[0033] Preparation of phosphate-intercalated modified strontium molybdate slow-release rust inhibitor: 10.00 g of ammonium heptamolybdate and 4.00 g of strontium chloride hexahydrate were dissolved in hot water at 80 °C. After mixing, the mixture was transferred to an autoclave and reacted at 155.0 °C for 8.0 hours. After reaction, the mixture was cooled, filtered, and the precipitate was washed with hot water until no chloride ions were found. The precipitate was then dried to obtain the precursor. 14.00 g of the precursor was weighed and ground together with 14.00 g of diammonium hydrogen phosphate and 3.00 g of urea for 50 minutes. The mixture was placed in a muffle furnace and calcined at 502.0 °C for 5.0 hours using the same procedure. After cooling in the furnace, the mixture was ground through a 400-mesh sieve to obtain the phosphate-intercalated modified strontium molybdate slow-release rust inhibitor.

[0034] Preparation of corrosion-resistant concrete for shield tunnel segments: Accurately weigh the following raw materials: 358.0g sulfoaluminate cement, 65.0g Grade I fly ash, 85.0g S95 grade slag powder, 11.0g of the aforementioned composite material, 5.0g of the aforementioned rust inhibitor, 728.0g manufactured sand, 475.0g 5-10mm crushed stone, and 715.0g 10-20mm crushed stone. Add all solid raw materials to a mixer and dry mix at 45±5 rpm for 55 seconds. Add a mixture consisting of 135.0g tap water, 4.90g polycarboxylate superplasticizer, and 0.35g defoamer, and wet mix at 60±5 rpm for 130 seconds to obtain a uniform slurry. The pouring and vibration processes are the same as in Example 1. After initial setting, steam curing is performed: the temperature is increased to 52.0℃ at a rate of 12℃ / h, and the temperature is maintained for 3.5 hours. Then, the temperature is reduced at a rate of 15℃ / h to the required temperature difference before demolding.

[0035] Comparative Example 1

[0036] The difference between this comparative example and Example 1 is that this comparative example does not contain the layered bimetallic hydroxide-aluminum silicate nanosheet composite and the phosphate intercalation modified strontium molybdate slow-release rust inhibitor.

[0037] Comparative Example 2

[0038] The difference between this comparative example and Example 1 is that this comparative example only adds a layered bimetallic hydroxide-aluminum silicate nanosheet composite.

[0039] Comparative Example 3

[0040] The difference between this comparative example and Example 1 is that this comparative example only adds phosphate intercalation modified strontium molybdate slow-release rust inhibitor.

[0041] The performance of corrosion-resistant concrete for shield tunnel segments obtained in Examples 1-3 and Comparative Examples 1-3 was tested in accordance with national and industry standard testing specifications.

[0042] Compressive strength: Concrete cube specimens with dimensions of 100mm × 100mm × 100mm were prepared and cured for 28 days under standard conditions of 20±2℃ and relative humidity ≥95%. A microcomputer-controlled electro-hydraulic servo pressure testing machine was used to apply pressure to the specimens at a loading rate of 0.5MPa / s until failure, and the peak load was recorded. The compressive strength was calculated by dividing the failure load by the bearing area, and the result was taken as the arithmetic mean of a set of three specimens.

[0043] Chloride ion migration coefficient: Concrete cylindrical specimens with a diameter of 100 mm × 50 mm were prepared and cured under standard conditions for 28 days. After sealing the sides of the specimens, they were placed in a vacuum desiccator, evacuated to an absolute pressure below 1 kPa and maintained for 3 hours, and then immersed in saturated Ca(OH)₂ solution for another 18 ± 2 hours. The salt-saturated specimens were installed in an RCM testing apparatus, with 0.3 mol / L NaOH solution injected at one end and 10% NaCl solution injected at the other end, and a 30V DC power supply was continuously applied for 24 hours. After the test, the specimens were split open, and 0.1 mol / L AgNO₃ solution was sprayed on the cross-section. The clear depth of the chloride ion penetration front was measured. The unsteady-state chloride ion migration coefficient was calculated according to the Nernst-Planck equation.

[0044] Electrical flux: Using cylindrical specimens of the same specifications as described above, after curing for 28 days, vacuum saturation was performed. The specimen was placed in a test cell, with one end injected with 3.0% NaCl solution and the other end with 0.3 mol / L NaOH solution, and a 60V DC voltage was applied. The current passing through the specimen over 6 hours was recorded using a data acquisition system, and the total charge passing through was calculated by integrating over time, which is the electrical flux value.

[0045] Sulfate corrosion resistance strength and corrosion resistance coefficient: 100 mm cube specimens were prepared, cured for 28 days, then immersed in 5.0% Na₂SO₄ solution for 16 hours, followed by drying in an oven at 80±5℃ for 6 hours, and then cooling at room temperature for 2 hours, constituting one wet-dry cycle. Mass change was measured after every 15 cycles. After 60 cycles, the compressive strength of the specimens was tested and compared with the strength of a standard-cured control specimen of the same age. The strength corrosion resistance coefficient is the percentage of the post-corrosion strength to the control strength.

[0046] Rapid carbonization depth: 100mm×100mm×400mm prism specimens were prepared and cured for 28 days before being placed in a carbonization chamber. The chamber environment was controlled as follows: temperature 20±2℃, relative humidity 70±5%, CO2 concentration 20±3%. After continuous exposure in this environment for 28 days, the specimens were removed and immediately split along the direction perpendicular to the casting surface. A 1% phenolphthalein ethanol solution was uniformly sprayed onto the split surface. After standing for 30 seconds, the vertical depth of the non-reddened area was measured. Six measuring points were selected at equal intervals on the cross-section, and the average value was taken.

[0047] Reinforcing steel corrosion current density: Concrete specimens with embedded Φ12mm×100mm plain round reinforcing bars were cast, with a protective layer thickness of 30mm, and cured under standard conditions for 28 days. All surfaces except the test surface were sealed with epoxy resin and then immersed in a 3.5% NaCl solution for an extended period. A three-electrode system was used, with the reinforcing steel bar as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum sheet as the auxiliary electrode. Using an electrochemical workstation, after the open-circuit potential stabilized, linear polarization was performed within the Ecorr ± 10mV range at a scan rate of 0.166mV / s. The polarization resistance Rp was calculated according to the Stern-Geary formula, and then the corrosion current density Icorr was obtained.

[0048] The performance test data above are shown in Table 1.

[0049] Table 1 Performance Test Results

[0050] The test results in Table 1 above clearly show that the concrete prepared in Examples 1-3 of this invention systematically and significantly solves the key technical problems of existing shield tunnel segment concrete in harsh corrosive environments by synergistically introducing layered bimetallic hydroxide-aluminum silicate nanosheet composite and phosphate intercalation modified strontium molybdate slow-release rust inhibitor.

[0051] Specifically, Comparative Example 1, as the baseline group without any modified compounds, had the lowest level in all durability indicators, for example, as high as 4.8 × 10⁻⁶. -12 The chloride ion migration coefficient is m² / s, the electrical flux at 2850C, and 5.60 × 10⁻⁶ m² / s. -8The corrosion current density of steel bars in A / cm² directly exposes the inherent defects of traditional high-performance concrete, even with the use of sulfate-resistant cement and mineral admixtures, which makes it difficult to effectively resist chloride ion penetration, sulfate erosion and steel bar corrosion. Its durability is insufficient to meet the extreme requirements of a 100-year design life.

[0052] Comparative Examples 2 and 3 respectively revealed the limitations of single-functional compounds: Comparative Example 2, which only added a layered complex, had a chloride ion migration coefficient of 1.9 × 10⁻⁶. -12 Although the current density (m² / s) and current flux (1250C) are significantly improved compared to Comparative Example 1, demonstrating its effectiveness in improving matrix density and adsorbing chloride ions, its current density for steel reinforcement corrosion (3.80 × 10⁻⁶ m² / s) is still lower than that of Comparative Example 1. -8 The A / cm² concentration was still much higher than that of the example group, indicating that a simple physical barrier cannot provide sufficient and durable electrochemical protection for the reinforcing steel. Once the corrosive medium breaks through the defense, steel corrosion will occur rapidly. In contrast, Comparative Example 3, which only added a slow-release corrosion inhibitor, had a steel corrosion current density (1.50 × 10⁻⁶). -8 The A / cm² value is relatively low, indicating a certain level of rebar protection capability, but its chloride ion migration coefficient (4.0×10⁻⁶) is low. -12 The m² / s and electrical flux (2600C) are still very high, indicating that it is impossible to prevent a large amount of corrosive media from rapidly penetrating into the concrete. The rust inhibitor will be in a high-concentration corrosive environment for a long time and may be consumed or become ineffective prematurely, making the protection difficult to last.

[0053] Embodiments 1-3 of the present invention successfully overcome the shortcomings of the aforementioned single technical path, achieving an organic combination of "active defense" and "passive blocking." Specifically, the embodiment group achieved a significantly better overall performance balance than all comparative examples: extremely low chloride ion migration coefficient (1.2-1.5×10⁻⁶). -12 The layered composite material significantly enhances the matrix's ability to hinder the migration of corrosive ions, as evidenced by its high current density (0.85-1.10×10⁻⁶ m² / s) and electrical flux (850-920C). Simultaneously, the ultra-low corrosion current density of the steel reinforcement (0.85-1.10×10⁻⁶ m² / s) demonstrates this. -8 The A / cm² (amount per square centimeter) demonstrates that the slow-release corrosion inhibitor can maintain the passive state of the reinforcing steel more persistently and efficiently in a reinforced matrix environment. Furthermore, the example group also exhibited excellent performance in resistance to sulfate attack (strength corrosion resistance coefficient 96-98%) and carbonization (depth 1.5-1.8 mm). This indicates that the two compounds produce a synergistic effect of "1+1>2": the densification and ion immobilization environment formed by the layered composite creates a milder and more stable working environment for the slow-release corrosion inhibitor, significantly reducing its functional load and thus achieving longer-lasting and more reliable protection; while the active protection provided by the corrosion inhibitor compensates for the risk that the physical barrier may fail due to micro-defects.

[0054] Therefore, this invention effectively solves the comprehensive technical problems in the prior art, namely, the insufficient impermeability of concrete matrix and the lack of long-term effectiveness and specificity of steel reinforcement protection measures (such as traditional rust inhibitors) and their inability to synergistically enhance each other. It provides a comprehensive solution for shield tunnel segment concrete that can resist chloride, sulfate and carbonation composite erosion in an all-round and long-term manner.

Claims

1. A method for preparing corrosion-resistant concrete for shield tunnel segments, characterized in that the steps include... include: S1. By weight, add 350-380 parts of sulfoaluminate cement, 50-70 parts of fly ash, 80-100 parts of slag powder, 8-12 parts of layered bimetallic hydroxide-alumina silicate nanosheet composite, 5-8 parts of phosphate intercalated modified strontium molybdate slow-release rust inhibitor, 720-750 parts of manufactured sand, 450-480 parts of 5-10mm crushed stone, and 680-720 parts of 10-20mm crushed stone to a mixer and dry mix. S2. Add 130-145 parts water, 4.8-6.5 parts polycarboxylate superplasticizer and 0.3-0.6 parts defoamer to the mixer, stir to obtain a mixed slurry; pour the mixed slurry into the mold and vibrate it; after the initial setting of the slurry, move the mold to the steam curing kiln; After a heating phase to 50-60℃, maintain a constant temperature, and then cool down to room temperature.

2. The method for preparing corrosion-resistant concrete for shield tunnel segments according to claim 1, characterized in that, In step S1, the dry mixing time is 30-60 seconds.

3. The method for preparing corrosion-resistant concrete for shield tunnel segments according to claim 1, characterized in that, In step S2, the constant temperature curing time is 2-4 hours.

4. The method for preparing corrosion-resistant concrete for shield tunnel segments according to claim 1, characterized in that, The preparation method of the layered bimetallic hydroxide-aluminum silicate nanosheet composite includes: A1, dissolving 10-14 parts by weight of magnesium nitrate hexahydrate and 4-8 parts by weight of aluminum nitrate nonahydrate in 180-220 parts by weight of deionized water to obtain mixed salt solution A; dissolving 5-6 parts by weight of sodium hydroxide and 4-5 parts by weight of anhydrous sodium carbonate in 90-110 parts by weight of deionized water to obtain mixed alkaline solution B; adding mixed alkaline solution B to mixed salt solution A under nitrogen protection and continuous stirring, and adjusting the pH... H is adjusted to 9.8-10.2, and crystallized and aged at 64-66℃. The slurry is collected by centrifugation and washed with deionized water until neutral to obtain a wet filter cake. A2. The wet filter cake is redispersed in 140-160 parts of an aqueous solution containing 2-4 parts of sodium silicate and 0.4-0.6 parts of hexadecyltrimethylammonium bromide. The mixture is then hydrothermally reacted in a high-pressure reactor at 118-122℃ to obtain the product. The product is centrifuged, washed, and vacuum dried at 78-82℃. After grinding, it is sieved.

5. The method for preparing corrosion-resistant concrete for shield tunnel segments according to claim 4, characterized in that, In step A1, the crystallization aging time at 64-66℃ is 18-20 hours.

6. The method for preparing corrosion-resistant concrete for shield tunnel segments according to claim 4, characterized in that, In step A2, the hydrothermal reaction at 118-122℃ takes 12-14 hours.

7. The method for preparing corrosion-resistant concrete for shield tunnel segments according to claim 1, characterized in that, The preparation method of the phosphate intercalation modified strontium molybdate slow-release rust inhibitor includes: B1, dissolving 6-10 parts by weight of ammonium heptamolybdate and 4-6 parts by weight of strontium chloride in hot water at 78-82℃ to obtain a mixture; transferring the mixture to a high-pressure reactor, reacting at 140-160℃, naturally cooling, filtering, obtaining a washing solution, washing the precipitate with deionized water to obtain the precursor strontium molybdate; grinding and mixing the precursor strontium molybdate with 14-16 parts by weight of diammonium hydrogen phosphate and 1-3 parts by weight of urea to obtain a mixture; B2, placing the mixture in a muffle furnace, calcining at 495-505℃ in an air atmosphere; naturally cooling after calcination to obtain a block product, crushing and grinding the block product.

8. The method for preparing corrosion-resistant concrete for shield tunnel segments according to claim 7, characterized in that, In step B1, the reaction time is 6-8 hours at 140-160℃.

9. The method for preparing corrosion-resistant concrete for shield tunnel segments according to claim 7, characterized in that, In step B2, the calcination time at 495-505℃ is 3-5 hours.

10. A corrosion-resistant concrete for shield tunnel segments, characterized in that, The corrosion-resistant concrete for shield tunnel segments is prepared according to the method described in any one of claims 1-9.

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