Cement-based grouting material resistant to stray current corrosion and preparation method thereof

Abstract

The application belongs to the technical field of underground engineering grouting materials, and more particularly relates to a cement-based grouting material resistant to stray current corrosion and a preparation method thereof. The cement-based grouting material resistant to stray current corrosion provided by the application overcomes the technical defects of the existing cement-based grouting material, such as weak resistance to stray current corrosion, easy agglomeration of modified components, easy loss of corrosion inhibitors, and the like. Based on the micro mechanism of stray current electrochemical corrosion, the application constructs a triple synergistic long-acting protection system of "passivation film slow-release protection + uniform conductive network shunting + nano-dense structure corrosion resistance", and effectively inhibits the damage behaviors of grouting body anodic oxidation, cathodic gas cracking, ion migration expansion and the like by optimizing the component ratio, introducing the carrier slow-release technology, adding the pre-dispersion process and perfecting the multi-dimensional performance evaluation system, thereby greatly improving the durability and construction stability of the material under the complex environment of subway stray current, water enrichment and ion coupling, and realizing the long-acting safe service of the tunnel grouting reinforcement structure.

Description

Technical Field

[0001] This invention belongs to the field of underground engineering grouting materials technology, and more specifically relates to a cement-based grouting material resistant to stray current corrosion and its preparation method. Background Technology

[0002] Urban subway tunnels generally adopt a DC power supply and track return operation mode. Due to factors such as rail insulation defects, groundwater seepage, and line length, stray currents cannot be completely returned through the rails and will continue to leak and spread to the tunnel lining, grouting reinforcement layer and surrounding rock system, forming a long-term, hidden and irreversible electrochemical corrosion environment, which is a unique cause of disease in the underground structure of subway tunnels.

[0003] Cement-based grouting materials, as key materials for reinforcing subway tunnel structures, sealing cracks, and waterproofing, are porous composite materials rich in alkaline pore solutions. They possess excellent electrical conductivity and are highly susceptible to becoming the primary corrosion carrier for stray currents. The damage caused by stray currents to the grout is essentially electrochemical corrosion, with the core destructive mechanism consisting of two polarity reactions and ion migration damage: the anodic region continuously consumes alkaline hydration products such as calcium hydroxide, leading to a decrease in the alkalinity of the grout and increased neutralization, gradually decomposing and destroying the cementitious system; the cathodic region undergoes a reduction reaction, continuously releasing hydrogen gas, which accumulates in the micropores, creating pore pressure and generating numerous microcracks; simultaneously, the electric field drives the directional migration of calcium, chloride, and sulfate ions, continuously generating expansive products such as ettringite and gypsum, ultimately leading to internal loosening of the grout, interconnected cracks, and structural collapse.

[0004] Existing ordinary cement-based grouting materials only have basic reinforcement and seepage prevention functions, and have not been systematically modified to address the stray current electrochemical corrosion characteristics. They have significant technical defects in the multi-field coupled service environment of subways: (1) Under the long-term action of stray current, the microstructure of the grout body continues to deteriorate, the porosity increases significantly, the density drops sharply, and the mechanical properties and seepage resistance decrease rapidly; (2) The grouting layer gradually loses its bonding and reinforcement capabilities, and cannot continuously block the leakage channels, which in turn causes tunnel settlement, excessive convergence deformation and other diseases, forming a vicious cycle of "stray current corrosion - grouting layer deterioration - leakage aggravation - corrosion upgrade", which seriously shortens the service life of the tunnel and threatens the operational safety.

[0005] Current grouting material modification technologies have significant limitations: most focus only on optimizing grout fluidity, conventional mechanical strength, and impermeability, without designing protection systems for the three core corrosion mechanisms of stray current anodic oxidation, cathodic gas generation, and ion migration. At the same time, existing conductive modification, nano-modification, and corrosion-inhibiting modification technologies have many engineering shortcomings. Direct addition of long carbon fibers is prone to agglomeration and failure; nanoparticles without dispersion treatment are prone to agglomeration; corrosion inhibitors are easily lost due to simple physical doping; compounded additives are prone to hydration conflicts; and crude preparation processes prevent modified components from exerting their effectiveness. Ultimately, the improvement in the material's electrochemical corrosion resistance is limited, and it cannot meet the long-term durability requirements of subway tunnels.

[0006] Therefore, developing a special grouting material that is suitable for the water-rich coupling environment of stray current in subways, has stable performance, and can be industrially promoted has become a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] This invention relies on the triple protection concept of "passivation protection, current shunting, and dense corrosion inhibition" to optimize the material composition ratio, modification mechanism, and preparation process. It solves the problems of modification failure, poor stability, and insufficient workability of existing technologies, and provides a cement-based grouting material resistant to stray current corrosion and its preparation method. It particularly relates to high-performance cement-based grouting materials and their preparation methods used in complex environments such as urban rail transit and tunnel engineering where stray current electrochemical corrosion, water-rich conditions, and multi-ion coupling are common.

[0008] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention: provides a cement-based grouting material resistant to stray current corrosion, comprising, by weight, the following raw materials: The ingredients are: 40-60 parts silicate cement, 15-25 parts fly ash, 10-20 parts slag powder, 5-10 parts silica fume, 3-8 parts stray current corrosion modifier, 0.5-1.5 parts water-reducing agent, 0.1-0.5 parts retarder, 2-5 parts expansion agent, 0.05-0.2 parts dispersant, and 30-40 parts water. The stray current corrosion resistant modifier includes calcium nitrate, sodium nitrite, aminopropyltriethoxysilane (APTES), surface-modified short-cut conductive carbon fibers, and nano-titanium dioxide.

[0009] Furthermore, the silicate cement is P.O 42.5 grade silicate cement.

[0010] Furthermore, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

[0011] Furthermore, the retarder is at least one selected from sodium gluconate, sodium citrate, sodium tartrate, potassium sodium tartrate, borax, sucrose, calcium lignosulfonate, sodium pyrophosphate, and sodium hexametaphosphate.

[0012] Optionally, the retarder is at least one of sodium gluconate, sodium citrate, and sodium tartrate.

[0013] Furthermore, the expanding agent is at least one of the following: ettringite-type expanding agent, ettringite-type expanding agent, calcium sulfoaluminate-type expanding agent, calcium oxide-type expanding agent, magnesium oxide-type expanding agent, ettringite-calcium oxide composite expanding agent, and calcium sulfoaluminate-calcium oxide composite expanding agent.

[0014] Optionally, the expanding agent is an ettringite-type expanding agent and / or an ettringite-calcium oxide composite expanding agent.

[0015] Furthermore, the dispersant is at least one selected from hydroxypropyl methylcellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, methylcellulose, polyvinylpyrrolidone, sodium polyacrylate, sodium hexametaphosphate, and sodium dodecylbenzenesulfonate.

[0016] Optionally, the dispersant is hydroxypropyl methylcellulose, or hydroxypropyl methylcellulose and polyvinylpyrrolidone, or hydroxypropyl methylcellulose and sodium carboxymethyl cellulose.

[0017] Furthermore, the mass ratio of calcium nitrate, sodium nitrite, aminopropyltriethoxysilane (APTES), surface-modified short-cut conductive carbon fiber, and nano-titanium dioxide is 35-45:22-28:12-18:8-12:8-12.

[0018] Furthermore, the surface-modified short-cut conductive carbon fiber has a length of 3-6 mm and is prepared by KH-550 modification.

[0019] Furthermore, the particle size of the nano-titanium dioxide is 20-50 nm.

[0020] The second technical solution of the present invention provides a method for preparing the above-mentioned cement-based grouting material resistant to stray current corrosion, comprising the following steps: Silicate cement, fly ash, slag powder and silica fume are dry-mixed evenly to obtain dry mix material; Nano-titanium dioxide was dispersed in 20 wt%-40 wt% dry mix to obtain uniformly dispersed nano-titanium dioxide. Surface-modified short-cut conductive carbon fibers, dispersant and water accounting for 15-30 wt% of the total water volume are mixed and dispersed evenly to obtain a carbon fiber suspension; Mix the remaining water, calcium nitrate, sodium nitrite, water-reducing agent, retarder, and expanding agent, and stir until completely dissolved to obtain a mixed solution; After the carbon fiber suspension is mixed evenly with the mixed solution, it is then mixed evenly with the remaining dry mix to obtain the cement-based grouting material resistant to stray current corrosion.

[0021] The third technical solution of the present invention provides an application of the above-mentioned cement-based grouting material resistant to stray current corrosion in tunnel grouting reinforcement engineering.

[0022] The present invention discloses the following technical effects: Significantly improved corrosion resistance: After 30 days of accelerated corrosion testing with 10V DC voltage, the compressive strength loss rate of the grouting material of this invention is only 10-15%, which is more than 60% higher than that of ordinary grouting materials (30-40%).

[0023] Highly dense microstructure: Mercury intrusion porosimetry (MIP) tests show that the most probable pore size is reduced from 50 nm to below 20 nm, and the total porosity is reduced by about 25%, effectively cutting off ion migration pathways.

[0024] Excellent electrochemical stability: Electrochemical impedance spectroscopy (EIS) shows a significant increase in charge transfer resistance and a positive shift in open circuit potential (OCP), indicating that the passivation film is stable and the corrosion current density is reduced.

[0025] Excellent construction performance: Through HPMC dispersion and step feeding process, the problem of fiber agglomeration is solved, the slurry fluidity is maintained at 260-270mm, the pumpability is excellent, and there is no risk of pipe blockage. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] Unless otherwise specified, all raw materials and reagents involved in the specific embodiments of this invention are commercially available products.

[0032] Unless otherwise specified, room temperature and normal temperature in the specific embodiments of this invention refer to 20-30℃.

[0033] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0034] The surface-modified short-cut conductive carbon fibers involved in the specific embodiments of the present invention have a length between 3 and 6 mm and are prepared through the following steps: (1) Place the short-cut conductive carbon fibers in a solvent (ethanol, acetone or deionized water, preferably acetone) and ultrasonically clean for 10-30 min (preferably 20 min) to remove impurities from the fiber surface, and then dry them at 60-80℃ (preferably 70℃) to obtain pretreated short-cut conductive carbon fibers. (2) The pretreated short-cut conductive carbon fiber is added to the oxidation modification liquid and stirred and oxidized at 50-80℃ (preferably 60℃) for 0.5-2 h (preferably 1 h) to form oxygen-containing active groups such as hydroxyl and carboxyl groups on the fiber surface; The oxidative modification solution is a nitric acid solution or a mixed acid solution composed of nitric acid and sulfuric acid (preferably a nitric acid solution). When the oxidative modification solution is a nitric acid solution, the concentration of the nitric acid solution is 20-30 wt%, preferably 25 wt%. When the oxidative modification solution is a mixed acid solution composed of nitric acid and sulfuric acid, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:3, and it is diluted to a total acid concentration of 40-50 wt%, preferably 40 wt%.

[0035] (3) The oxidized short-cut conductive carbon fibers are repeatedly washed with deionized water until the pH value of the washing solution is 6-8 (preferably 7), and then dried at 60-80℃ (preferably 70℃) to obtain surface-activated short-cut conductive carbon fibers. (4) Add aminopropyltriethoxysilane (KH-550) to an ethanol-water mixture (volume ratio 9:1) and adjust the pH to 4-5 (preferably 4), hydrolyze for 20-40 min (preferably 30 min) to obtain a silane coupling modified solution; (5) Add the surface-activated short-cut conductive carbon fiber to the silane coupling modification liquid, stir or ultrasonically disperse for 30-60 min (preferably 45 min), so that aminopropyltriethoxysilane is grafted onto the surface of the short-cut conductive carbon fiber to form an organic-inorganic interface coupling layer. (6) After filtering and washing the grafted short-cut conductive carbon fiber, dry it at 60-80℃ (preferably 70℃) for 2-6 h (preferably 4 h) to obtain the surface-modified short-cut conductive carbon fiber.

[0036] The surface-modified short-cut conductive carbon fibers used in the specific embodiments of the present invention are prepared by the preferred parameters in the above method.

[0037] The particle size of the nano-titanium dioxide involved in the specific embodiments of the present invention is between 20-50 nm.

[0038] In some specific embodiments, the present invention provides a method for preparing a cement-based grouting material resistant to stray current corrosion, employing a stepwise pre-dispersion + high-speed shear composite process, the steps of which include: S1. Prepare the following raw materials according to the mass fractions: 40-60 parts of silicate cement (P・O 42.5 grade silicate cement), 15-25 parts of fly ash, 10-20 parts of slag powder, 5-10 parts of silica fume, 3-8 parts of stray current corrosion resistant modifier, 0.5-1.5 parts of water-reducing agent (polycarboxylate-based high-efficiency water-reducing agent), 0.1-0.5 parts of retarder (sodium gluconate), 2-5 parts of expansive agent (ettringite-type expansive agent), 0.05-0.2 parts of dispersant (hydroxypropyl methylcellulose), and 30-40 parts of water; The stray current corrosion resistant modifier consists of calcium nitrate, sodium nitrite, aminopropyltriethoxysilane (KH-550, APTES), surface-modified short-cut conductive carbon fibers, and nano-titanium dioxide in a mass ratio of 35-45:22-28:12-18:8-12:8-12.

[0039] Calcium nitrate replenishes calcium ions lost in the anode region and promotes early hydration; APTES improves the fiber interface and forms a hydrophobic barrier; nano-titanium dioxide.

[0040] S2. Dry mix silicate cement, fly ash, slag powder and silica fume for 3-5 minutes to obtain a dry mix; S3. Take 20 wt%-40 wt% of the total dry mix and mix it with nano titanium dioxide. Dry mix at high speed (1000-1500 rpm) for 2 minutes to obtain uniformly dispersed nano titanium dioxide.

[0041] In this step, the physical isolation effect of fine powder particles is used to prevent the agglomeration of nano-titanium dioxide.

[0042] S4. Mix the surface-modified short-cut conductive carbon fibers, dispersant and water accounting for 15-30 wt% of the total water volume, and use a high-speed shear mixer (speed ≥3000 rpm) to shear and disperse for 3-5 min to form a uniform and stable carbon fiber suspension.

[0043] S5. Mix the remaining water, calcium nitrate, sodium nitrite, water-reducing agent, retarder, and expanding agent, and stir until completely dissolved to obtain a mixed solution.

[0044] S6. Add the carbon fiber suspension to the mixed solution and stir at low speed (300-500 rpm) for 1 minute to mix evenly. Then mix with the remaining dry mix material and stir at low speed (300-500 rpm) for 2 minutes to fully wet the material. Then stir at high speed (1200-1800 rpm) for 3-5 minutes until a uniform, fine, and non-agglomerated grout is formed, thus obtaining a cement-based grouting material resistant to stray current corrosion.

[0045] Existing general-purpose cement-based grouting materials and conventional modified grouting materials can only meet the basic reinforcement and seepage prevention needs of ordinary underground engineering projects. They suffer from defects such as a single protection mechanism, failure of modified components, poor process adaptability, and insufficient durability, and cannot adapt to the stray current electrochemical corrosion environment unique to subways. The stray current corrosion resistant cement-based grouting material provided by this invention overcomes the technical defects of existing cement-based grouting materials, such as weak stray current corrosion resistance, easy agglomeration and failure of modified components, and easy loss of corrosion inhibitors. Based on the microscopic mechanism of stray current electrochemical corrosion, this invention constructs a triple synergistic long-term protection system of "passivation film slow-release protection + uniform conductive network current diversion + nano-dense structure corrosion inhibition". By optimizing the component ratio, introducing carrier slow-release technology, adding pre-dispersion process, and improving multi-dimensional performance evaluation system, it effectively inhibits destructive behaviors such as anodic oxidation, cathodic gas generation cracking, and ion migration and expansion of grout body, and significantly improves the durability and construction stability of the material in the complex environment of stray current, water-rich, and multi-ion coupling in subways, so as to achieve long-term safe service of tunnel grouting reinforcement structures.

[0046] The core innovation of this invention lies in optimizing and upgrading the triple synergistic long-term protection system, while simultaneously solving the process defects and stability problems of traditional modification technologies. The core principle is as follows: Organic-Inorganic Hybrid Slow-Release Passivation Protection (Long-Term Inhibition of Anodic Corrosion): This invention abandons the traditional simple physical adsorption slow-release mode and constructs a scientifically stable hybrid corrosion inhibition protection system. The sodium nitrite dosage is limited, and the critical corrosion inhibition concentration is determined through electrochemical polarization curve testing, avoiding the risks of cement hydration disorder and environmental toxicity caused by high dosage. Silica fume, as a porous carrier, utilizes its rich microporous structure to physically anchor and load calcium nitrate and sodium nitrite corrosion inhibitors through a weak electrostatic adsorption method. Compared with nano-titanium dioxide, it can effectively avoid the ion desorption problem in highly alkaline porous solutions (pH > 12.5), achieving long-term slow and controllable release of the corrosion inhibitor. Simultaneously, it is combined with an aminopropyltriethoxysilane coupling agent, which, after hydrolysis, forms a dense hydrophobic film in the matrix pores and material interfaces, doubly blocking the migration of moisture and corrosive ions, continuously maintaining the integrity of the passivation film on the surface of the reinforcing steel and cement system, and blocking anodic electrochemical corrosion from the source.

[0047] Threshold-controllable uniform three-dimensional conductive network protection (eliminating local current concentration): Utilizing 3-6mm surface-modified short-cut conductive carbon fibers, combined with a composite process of "dry material physical isolation + special surfactant liquid-phase dispersion," it completely solves the defects of long fiber agglomeration, clumping, and flocculation. The conductive percolation threshold is precisely calibrated through resistivity gradient testing, ensuring that a continuous, uniform, and stable three-dimensional conductive network can be constructed even at a low dosage of 0.1%-0.5%. This effectively and uniformly diverts stray currents, reduces local current density, eliminates violent electrochemical reactions caused by current hotspots, and inhibits hydrogen accumulation and micropore pressure cracking in the cathode area. Simultaneously, it avoids the thickening side effects of traditional HPMC dispersants, ensuring excellent pumpability of the slurry and achieving a balance between conductivity and workability.

[0048] Full-process controlled dispersion of dense nano-sized corrosion inhibitors (completely blocking ion migration): Addressing the challenge of secondary agglomeration of nano-titanium dioxide upon adding water, the dispersion process has been optimized and improved. A full-process controlled dispersion process of "dry material premixing and isolation + step-by-step feeding + high-speed composite stirring" completely solves the problem of nanoparticle agglomeration failure. It fully leverages the micro-filling and nucleation-inducing effects of nano-titanium dioxide to precisely fill the micropores inside the matrix, refine the pore size, and cut off connecting pore channels, significantly reducing the matrix porosity and permeability coefficient. This effectively inhibits the directional migration of eroding ions driven by the electric field and prevents the formation of expansive corrosion products.

[0049] Hydration Synergistic Stability Control: Optimize the distribution ratio of calcium nitrate early strength component and sodium gluconate retarder component to accurately balance the hydration rate, avoid construction defects such as flash setting and excessive retarding, and ensure that the setting time of the grout is controllable and the workability is excellent.

[0050] Example 1 A method for preparing cement-based grouting materials resistant to stray current corrosion employs a stepwise pre-dispersion + high-speed shear composite process, the steps of which include: S1. Prepare the following raw materials according to the mass fractions: 50 parts of silicate cement (P・O 42.5 grade silicate cement), 20 parts of fly ash (Grade I fly ash), 15 parts of slag powder (Grade S95 slag powder), 8 parts of silica fume, 5 parts of stray current corrosion resistant modifier, 1 part of water-reducing agent (polycarboxylate-based high-efficiency water-reducing agent), 0.3 parts of retarder (sodium gluconate), 3 parts of expansion agent (ettringite-type expansion agent), 0.1 parts of dispersant (hydroxypropyl methylcellulose), and 35 parts of water; The stray current corrosion resistant modifier consists of calcium nitrate, sodium nitrite, aminopropyltriethoxysilane (APTES), surface-modified short-cut conductive carbon fibers, and nano-titanium dioxide in a mass ratio of 40:25:15:10:10.

[0051] S2. Dry mix silicate cement, fly ash, slag powder and silica fume for 4 minutes to obtain a dry mix; S3. Take 30 wt% of the total dry mix and mix it with nano titanium dioxide. Dry mix at high speed (1200 rpm) for 2 min to obtain uniformly dispersed nano titanium dioxide.

[0052] S4. Mix the surface-modified short-cut conductive carbon fibers, dispersant and water accounting for 20 wt% of the total water volume, and shear and disperse them for 4 min using a high-speed shear mixer (3000 rpm) to form a uniform and stable carbon fiber suspension.

[0053] S5. Mix the remaining water, calcium nitrate, sodium nitrite, water-reducing agent, retarder, and expanding agent, and stir until completely dissolved to obtain a mixed solution.

[0054] S6. Add the carbon fiber suspension to the mixed solution and stir at low speed (400 rpm) for 1 min to mix evenly. Then mix with the remaining dry mix material and stir at low speed (400 rpm) for 2 min to fully wet the material. Then stir at high speed (1500 rpm) for 4 min until a uniform, fine, and non-agglomerated grout is formed, thus obtaining a cement-based grouting material resistant to stray current corrosion.

[0055] Example 2 A method for preparing cement-based grouting materials resistant to stray current corrosion employs a stepwise pre-dispersion + high-speed shear composite process, the steps of which include: S1. Prepare the following raw materials according to the mass fractions: 45 parts of silicate cement (P・O 42.5 grade silicate cement), 25 parts of fly ash (Grade II fly ash), 18 parts of slag powder (Grade S105 slag powder), 6 parts of silica fume, 6 parts of stray current corrosion resistant modifier, 1.2 parts of water-reducing agent (polycarboxylate-based high-efficiency water-reducing agent), 0.4 parts of retarder (sodium gluconate), 4 parts of expansion agent (ettringite-type expansion agent), 0.15 parts of dispersant (hydroxypropyl methylcellulose), and 38 parts of water; The stray current corrosion resistant modifier consists of calcium nitrate, sodium nitrite, aminopropyltriethoxysilane (APTES), surface-modified short-cut conductive carbon fibers, and nano-titanium dioxide in a mass ratio of 42:24:14:11:9.

[0056] S2. Dry mix silicate cement, fly ash, slag powder and silica fume for 4 minutes to obtain a dry mix; S3. Take 30 wt% of the total dry mix and mix it with nano titanium dioxide. Dry mix at high speed (1200 rpm) for 2 min to obtain uniformly dispersed nano titanium dioxide.

[0057] S4. Mix the surface-modified short-cut conductive carbon fibers, dispersant and water accounting for 20 wt% of the total water volume, and shear and disperse them for 4 min using a high-speed shear mixer (3000 rpm) to form a uniform and stable carbon fiber suspension.

[0058] S5. Mix the remaining water, calcium nitrate, sodium nitrite, water-reducing agent, retarder, and expanding agent, and stir until completely dissolved to obtain a mixed solution.

[0059] S6. Add the carbon fiber suspension to the mixed solution and stir at low speed (400 rpm) for 1 min to mix evenly. Then mix with the remaining dry mix material and stir at low speed (400 rpm) for 2 min to fully wet the material. Then stir at high speed (1500 rpm) for 4 min until a uniform, fine, and non-agglomerated grout is formed, thus obtaining a cement-based grouting material resistant to stray current corrosion.

[0060] Comparative Example 1 The preparation steps for ordinary cement-based grouting materials include: S1. Prepare the following raw materials according to the mass fractions: 70 parts of silicate cement (P・O 42.5 grade silicate cement), 20 parts of fly ash (Grade I fly ash), 10 parts of slag powder (Grade S95 slag powder), 1 part of water-reducing agent (polycarboxylate-based high-efficiency water-reducing agent), 0.3 parts of retarder (sodium gluconate), and 35 parts of water.

[0061] S2. Mix the raw materials and stir evenly to obtain ordinary cement-based grouting material.

[0062] Test case The grouting material from the examples and comparative examples was injected into the mold and cured under standard conditions of temperature 20±1℃ and relative humidity not less than 90% until the specified age.

[0063] Performance tests were conducted according to the following criteria, and the results are shown in Table 1: 28-day compressive strength: The test was conducted strictly in accordance with the relevant provisions of GB / T 17671-2021, "Test Method for Strength of Cement Mortar (ISO Method)". The grouting materials prepared in each example and comparative example were molded into 40 mm × 40 mm × 160 mm prism specimens and cured for 28 days under standard curing conditions of 20 ± 1℃ and relative humidity not less than 90%. Compressive strength tests were then performed. At least three specimens were used in each group, and the test results were taken as the average value of the test values ​​of the same group of specimens.

[0064] 28-Day Water Permeability Pressure: Based on the relevant provisions of the "Standard for Test Methods of Long-Term Performance and Durability of Concrete" GB / T 50082-2024 regarding water permeability testing, the water permeability pressure of 28-day-old specimens was determined using a step-by-step pressure increase method. Before testing, the specimens were cured to 28 days, installed in the water permeability testing apparatus, and the water pressure was increased step-by-step as specified, observing the water seepage at the end faces and sides of the specimens. The water pressure at the level preceding the point where water seepage occurred was taken as the water permeability pressure of that group of specimens; if the specimen maintained the set pressure for the specified time without water seepage, it was determined that it met the water permeability requirements at that pressure level.

[0065] Electrochemical impedance spectroscopy (EIS) testing: Considering that cement-based grouting materials are porous ionic conductors, unlike metallic electronic conductors, a three-electrode system was employed. A metal electrode pre-embedded in the grouting body or a conductive reinforcing phase in full contact with the grouting body served as the working electrode; a saturated calomel electrode or silver / silver chloride electrode served as the reference electrode; and a platinum sheet electrode served as the counter electrode. After curing for 28 days, the specimens were placed in a simulated water-rich, multi-ion environment solution from a subway system for testing. The simulated solution may contain typical groundwater ion components such as chloride, sulfate, calcium, and sodium ions to simulate the water-rich, multi-ion coupled service environment of subway tunnels.

[0066] The preferred frequency range for electrochemical impedance spectroscopy is 10. 5 Hz to 10 -2 The AC disturbance amplitude is preferably 5-10 mV. Parameters such as pore solution resistance, charge transfer resistance, and interfacial film resistance are obtained through equivalent circuit fitting and used to evaluate the internal ion migration resistance of the grouting material, the stability of the interfacial passivation film, and the current shunting effect of the conductive network. The corrosion current density in Table 1 is the equivalent corrosion current density calculated from electrochemical monitoring results under a specific pre-embedded metal electrode system. It is used to characterize the corrosion tendency of the metal reinforcement phase or interfacial electrode in this system and does not indicate that the cement-based grouting material itself has undergone anodic dissolution corrosion.

[0067] Dynamic DC Accelerated Corrosion Test: To simulate the long-term effects of train start-stop, traction return current fluctuations, and stray current direction changes on the grouting body during subway operation, this invention employs a dynamic pulsed DC accelerated corrosion test. The specimen, cured for 28 days, is placed in a solution simulating the water-rich, multi-ion environment of a subway system. Conductive electrodes are placed at both ends of the specimen or at predetermined locations, and a periodic pulsed DC voltage of ±2 V to ±4 V is applied. One cycle consists of 30 seconds of energization followed by 10 seconds of de-energization, or an alternating positive and negative pulse method is used for accelerated corrosion, accumulating for 30 days. This dynamic pulsed electric field simulates the fluctuation and direction changes of stray currents in the subway system, avoiding excessively high constant voltage that could lead to severe water electrolysis, abnormal local pH values, and rapid damage under non-service conditions. After the dynamic DC accelerated corrosion is completed, the specimen is removed, surface moisture is wiped off, and the appearance damage, crack development, and edge peeling are observed and recorded. Subsequently, the compressive strength after corrosion is tested, and the compressive strength loss rate is calculated using the following formula: Compressive strength loss rate = (compressive strength 28 days before corrosion - compressive strength after 30 days of dynamic DC corrosion) / compressive strength 28 days before corrosion × 100%.

[0068] Table 1 As can be seen from Table 1, the stray current corrosion resistant cement-based grouting materials prepared in Examples 1 and 2 of the present invention, while maintaining good mechanical properties, have significantly better impermeability, electrochemical stability, and strength retention after dynamic DC current action than Comparative Example 1. This indicates that the composite modification system used in the present invention does not improve a single property, but forms multiple synergistic protective effects under stray current, water-rich and multi-ion coupling environments.

[0069] From the 28-day compressive strength perspective, the compressive strengths of Example 1 and Example 2 were 45.2 MPa and 42.8 MPa, respectively, which are at the same level as the 43.5 MPa of Comparative Example 1. This indicates that the introduction of calcium nitrate, sodium nitrite, APTES, surface-modified short-cut conductive carbon fibers, and nano-titanium dioxide did not weaken the basic load-bearing capacity of the cement-based grouting material. Specifically, the compressive strength of Example 1 was higher than that of Comparative Example 1, indicating that the promoting effect of calcium nitrate on early hydration, the pozzolanic reaction of slag powder and silica fume, the nucleation-inducing effect of nano-titanium dioxide, and the micro-reinforcing effect of short-cut carbon fibers can work together to promote the formation of hydration products and improve the integrity of the matrix structure.

[0070] From the 28-day seepage resistance pressure, Examples 1 and 2 reached 1.8 MPa and 1.7 MPa respectively, significantly higher than Comparative Example 1's 1.2 MPa, representing increases of approximately 50.0% and 41.7% respectively. This result indicates that silica fume, slag powder, fly ash, and nano-titanium dioxide in this invention can play a multi-scale particle filling role, refining the internal pore size of the grout body and reducing the proportion of interconnected pores. Simultaneously, the APTES-pretreated short-cut conductive carbon fibers have better interfacial bonding with cement hydration products, reducing potential interfacial defects and weak seepage zones after fiber incorporation, thereby jointly improving the seepage resistance of the grout body.

[0071] Based on the equivalent corrosion current density under a specific pre-embedded metal electrode system, Examples 1 and 2 are 0.28 μA·cm⁻¹. -2 and 0.31 μA·cm -2 This is significantly lower than the 0.92 μA·cm⁻¹ of Comparative Example 1. -2 Compared to Comparative Example 1, the corrosion rates were reduced by approximately 69.6% and 66.3%, respectively. These results demonstrate that, under simulated water-rich, multi-ion environment and electrochemical monitoring system conditions in a subway, the material of this invention can effectively reduce the tendency for interfacial corrosion. This is because: sodium nitrite and calcium nitrate help maintain the alkaline environment of the pore liquid and the passivation state of the interface; APTES forms an organic-inorganic coupling layer at the fiber-matrix interface and improves interfacial density; surface-modified short-cut conductive carbon fibers construct a more uniform conductive network to disperse local current concentration; and nano-titanium dioxide further refines the pore structure and inhibits the migration of corrosive ions. These effects collectively reduce the intensity of local electrochemical reactions, demonstrating a synergistic effect between passivation protection, conductive current diversion, and dense corrosion inhibition.

[0072] The compressive strength loss rates after 30 days of dynamic DC corrosion were 12.5% ​​and 11.8% for Examples 1 and 2, respectively, significantly lower than the 35.2% of Comparative Example 1, and reduced by approximately 64.5% and 66.5% compared to Comparative Example 1. This indicates that under the combined effects of a dynamic pulsed DC electric field and a water-rich, multi-ion environment, Comparative Example 1, lacking a specialized protection system against stray current corrosion, is prone to pore liquid ion migration, enhanced local electrochemical reactions, decomposition of hydration products, and microcrack propagation, leading to rapid strength decay after corrosion. In contrast, the material of this invention, through the stabilization of the passivation environment by corrosion-inhibiting components, the homogenization of current distribution by conductive carbon fibers, the refinement of pore structure by nano-titanium dioxide, and the continuous improvement of the composition of hydration products by mineral admixtures, effectively delays the structural deterioration process under the action of the electric field, thereby maintaining higher post-corrosion strength.

[0073] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0074] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cement-based grouting material resistant to stray current corrosion, characterized in that, By weight, the raw materials include: The ingredients are: 40-60 parts silicate cement, 15-25 parts fly ash, 10-20 parts slag powder, 5-10 parts silica fume, 3-8 parts stray current corrosion modifier, 0.5-1.5 parts water-reducing agent, 0.1-0.5 parts retarder, 2-5 parts expansion agent, 0.05-0.2 parts dispersant, and 30-40 parts water. The stray current corrosion resistant modifier includes calcium nitrate, sodium nitrite, aminopropyltriethoxysilane, surface-modified short-cut conductive carbon fibers, and nano-titanium dioxide.

2. The cement-based grouting material as described in claim 1, characterized in that, The silicate cement is P.O 42.5 grade silicate cement.

3. The cement-based grouting material as described in claim 1, characterized in that, The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

4. The cement-based grouting material as described in claim 1, characterized in that, The retarder is at least one of sodium gluconate, sodium citrate, sodium tartrate, potassium sodium tartrate, borax, sucrose, calcium lignosulfonate, sodium pyrophosphate, and sodium hexametaphosphate.

5. The cement-based grouting material as described in claim 1, characterized in that, The expanding agent is at least one of the following: ettringite-type expanding agent, ettringite-type expanding agent, calcium sulfoaluminate-type expanding agent, calcium oxide-type expanding agent, magnesium oxide-type expanding agent, ettringite-calcium oxide composite expanding agent, and calcium sulfoaluminate-calcium oxide composite expanding agent. And / or, the dispersant is at least one selected from hydroxypropyl methylcellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, methylcellulose, polyvinylpyrrolidone, sodium polyacrylate, sodium hexametaphosphate, and sodium dodecylbenzenesulfonate.

6. The cement-based grouting material as described in claim 1, characterized in that, The mass ratio of calcium nitrate, sodium nitrite, aminopropyltriethoxysilane, surface-modified short-cut conductive carbon fiber, and nano-titanium dioxide is 35-45:22-28:12-18:8-12:8-12.

7. The cement-based grouting material as described in claim 1, characterized in that, The surface-modified short-cut conductive carbon fibers have a length of 3-6 mm and are prepared by KH-550 modification.

8. The cement-based grouting material as described in claim 1, characterized in that, The particle size of the nano-titanium dioxide is 20-50 nm.

9. A method for preparing a cement-based grouting material resistant to stray current corrosion as described in any one of claims 1-8, characterized in that the step... include: Silicate cement, fly ash, slag powder and silica fume are dry-mixed evenly to obtain dry mix material; Nano-titanium dioxide was dispersed in 20 wt%-40 wt% dry mix to obtain uniformly dispersed nano-titanium dioxide. Surface-modified short-cut conductive carbon fibers, dispersant and water accounting for 15-30 wt% of the total water volume are mixed and dispersed evenly to obtain a carbon fiber suspension; Mix the remaining water, calcium nitrate, sodium nitrite, water-reducing agent, retarder, and expansion agent, and stir until completely dissolved to obtain a mixed solution; After the carbon fiber suspension is mixed evenly with the mixed solution, it is then mixed evenly with the remaining dry mix to obtain the cement-based grouting material resistant to stray current corrosion.

10. The application of a cement-based grouting material resistant to stray current corrosion as described in any one of claims 1-8 in tunnel grouting reinforcement engineering.

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