Rust prevention methods for steel materials

Abstract

A rust prevention method for a steel material according to the present application inhibits the corrosion of the steel material due to the adhesion of salt by including a step for directly applying a rust prevention agent comprising a resin, and a layered double hydroxide represented by the chemical formula M2+ 1-xM3+ x(OH)2(NO3 -)x / n・mH2O (M2+ is a bivalent metal, M3+ a trivalent metal; n is a natural number) to a steel material to which salt content has attached.

Description

Technical Field

[0001] The present invention relates to a method for preventing rust of steel materials.

Background Art

[0002] Reinforced concrete is a structure that combines high-tensile-strength reinforcing bars and high-compressive-strength concrete. Although the reinforcing bars are prone to oxidation and rusting, a passive film is formed on the surface of the reinforcing bars by the highly alkaline cement contained in the concrete. Therefore, the reinforcing bars inside the concrete do not corrode and can continue to meet the required performance.

[0003] However, when cracks or the like occur on the surface of the concrete, oxygen, moisture, etc. penetrate from the cracked portion, and a vicious cycle of further rusting occurs. Therefore, in order to prevent the deterioration of reinforced concrete, a resinous coating material is applied to the surface of the concrete (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the reinforcing bars are corroded by salt damage, the concrete covering the corroded reinforcing bars may be chiseled to expose the reinforcing bars, and a rust preventive agent may be applied to the surface of the reinforcing bars. As the rust preventive agent, for example, those containing nitrite ions (NO2 - ) are known. By using this type of rust preventive agent, a passive film (Fe2O3) is formed by the reaction of nitrite ions (NO2 - ) and iron ions (Fe 2+ ), and the corrosion of the reinforcing bars is suppressed.

[0006] However, since nitrite ions (NO2 - ) are used in an aqueous solution, there is a risk of human exposure and environmental impact (leakage).

[0007] An object of the present invention is to provide a rust prevention method for steel materials capable of suppressing corrosion of steel materials by salts.

Means for Solving the Problems

[0008] The rust prevention method for steel materials according to the present invention is to apply directly a rust preventive agent having a resin and a layered double hydroxide represented by the chemical formula M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n ·mH2O (where M 2+ represents a divalent metal, M 3+ represents a trivalent metal, and 0 < x < 1, m is a number greater than 0, n is a natural number) to a steel material to which salts have adhered. and a step of covering the steel material with a concrete material while the rust inhibitor starts to cure until it is completely cured.

Effects of the Invention

[0009] According to the present invention, corrosion of steel materials by salts can be suppressed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0011] The following describes a method for preventing rust on steel materials according to one embodiment.

[0012] (Regarding rust inhibitors) First, the rust inhibitor used in this embodiment will be described. The rust inhibitor in this embodiment contains a resin that functions as a binder and a layered double hydroxide.

[0013] (resin) The resin can be any liquid resin that can coat the surface of concrete or reinforcing steel, and that can prevent external moisture, chlorine, etc. from coming into contact with the coated surface. Examples of resins that can be used include epoxy resins, acrylic resins, and urethane resins. These resins may be used individually or in combination of two or more. The resin may also be a one-component or two-component resin.

[0014] (Epoxy resin) Examples of epoxy resins that can be used include bisphenol A type epoxy resin, halogenated bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin, and cresol novolac type epoxy resin.

[0015] Examples of bisphenol A type epoxy resins include condensate polymers of bisphenol A type diglycidyl ethers such as bisphenol A diglycidyl ether, bisphenol A polypropylene oxide diglycidyl ether, bisphenol A ethylene oxide diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, and hydrogenated bisphenol A propylene oxide diglycidyl ether. Such epoxy resins can be used individually or in combination of two or more types.

[0016] Furthermore, reactive diluents can be added to and blended into epoxy resins. Such reactive diluents are effective in reducing the viscosity of the composition. As such reactive diluents, compounds having one epoxy group in their molecule, such as phenyl glycidyl ether, butyl glycidyl ether, allyl glycidyl ether, styrene oxide, and octylene oxide, can be used. Such reactive diluents can be blended in an amount of preferably 45% by weight or less, and preferably 25% by weight or less, per the main component.

[0017] Furthermore, epoxy resins can also be formulated with additives that do not have epoxy groups but can react with components of the curing agent (such as amine compounds). Such compounds include isocyanates such as hexamethylene diisocyanate and tolylene diisocyanate, as well as α,β-unsaturated carbonyl compounds that undergo Michael addition reactions with amine compounds, such as acrylic acid esters and acrylamide derivatives. Acrylic acid esters are effective in improving low-temperature curing properties, while acrylamide derivatives are effective in improving thixotropy or adhesion. Such additives can be incorporated in an amount of preferably 30% by weight or less, more preferably 20% by weight or less, per the main component.

[0018] Furthermore, epoxy resins can also be appropriately formulated with other components such as plasticizers, dyes, organic pigments, inorganic fillers, polymer compounds, antioxidants, UV absorbers, coupling agents, and surfactants.

[0019] (Acrylic resin) As acrylic resins, for example, polymers of acrylic monomers or copolymers of acrylic monomers and other monomers can be used. Examples of acrylic monomers include C1-10 alkyl esters of (meth)acrylates such as (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, t-butyl (meth)acrylate, and hexyl (meth)acrylate, C3-12 cycloalkyl esters of (meth)acrylates such as cyclohexyl (meth)acrylate, aryl esters of (meth)acrylates such as phenyl (meth)acrylate, aralkyl esters of (meth)acrylates such as benzyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 3-hydroxyethyl (meth)acrylate. Examples include hydroxy C2-6 alkyl(meth)acrylates such as hydroxypropyl(meth)acrylate, alkylamino-alkyl(meth)acrylates such as dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate, and diethylaminopropyl(meth)acrylate, (meth)acrylamides or their derivatives such as (meth)acrylamide, N-methyl(meth)acrylamide, methylol(meth)acrylamide, and alkoxymethyl(meth)acrylamide, epoxy group-containing(meth)acrylates such as glycidyl(meth)acrylate, and (meth)acrylonitrile.

[0020] Examples of monomers copolymerized with acrylic monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, pt-butylstyrene, and vinyltoluene; fatty acid vinyl SL monomers such as vinyl propionate; unsaturated polycarboxylic acids such as maleic anhydride, maleic acid, fumaric acid, and itaconic acid, or esters of unsaturated polycarboxylic acid derivatives such as dimethyl maleate and diethyl fumarate; N-substituted maleimides such as N-phenylmaleimide; and olefin monomers such as ethylene and propylene. These monomers may be used individually or in combination of two or more.

[0021] (Urethane resin) As the urethane resin, for example, a urethane prepolymer having free isocyanate groups obtained by reacting a polyol with a polyisocyanate can be used.

[0022] Examples of polyols that can be used include polyether polyols and polyolefin polyols.

[0023] As polyether polyols, it is appropriate to use polyalkylene polyols having 2 to 4 hydroxyl groups (active hydrogen groups) in the molecule, obtained by addition polymerization of ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, or other alkylene oxides having 2 to 8 carbon atoms, preferably with 2 to 6 hydroxyl groups, to polyols having 2 to 8 carbon atoms, such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, glycerin, hexanediol, hexanetriol, glycerin, trimethylolpropane, and pentaerythritol, in the presence of an alkaline catalyst.

[0024] Suitable polyolefin polyols include, for example, polydiene polyols having 2 to 4 hydroxyl groups in the molecule, obtained by addition polymerization of a diene compound such as butadiene or isoprene with an alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran. Suitable polyisocyanates include compounds having 2 or more, preferably 2 to 3, isocyanate groups in one molecule.

[0025] Examples of the polyisocyanate include isocyanate compounds such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diphenyl diisocyanate, carbodiimide-modified diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, metaxylylene diisocyanate, 1,5-naphthalene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated toluylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate; burette polyisocyanate compounds such as Sumidule N (trade name of Sumitomo Bayer Urethane Co., Ltd.); polyisocyanate compounds having an isocyanate ring such as Desmodur IL, HL (trade names of Bayer A.G.), Coronate E.H. (trade name of Nippon Polyurethane Industry Co., Ltd.); and adduct polyisocyanate compounds such as Sumidule L (trade name of Sumitomo Bayer Urethane Co., Ltd.), Coronate HL (trade name of Nippon Polyurethane Industry Co., Ltd.). These polyisocyanates can be used alone or as a mixture of two or more.

[0026] (Layered double hydroxide) The layered double hydroxide is represented by the chemical formula M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n ·mH2O. Here, M 2+ represents a divalent metal, M 3+ represents a trivalent metal, and n is a natural number. Also, x is a number in the range of 0 < x < 1, and generally a number in the range of 1 / 6 < x < 1 / 3. m is a number greater than 0. This layered double hydroxide is sometimes called a hydrotalcite-like compound. Examples of the divalent metal ion (M 2+ ) include Mg 2+ , Fe 2+ , Zn 2+ , Li 2+ , Ni 2+ , Co 2+ , Cu 2+These are some examples. Also, trivalent metal ions (M 3+ For example, Al 3+ Fe 3+ , Cr 3+ Mn 3+ These are some examples. Furthermore, the divalent metal ions (M) included in the above general formula are also included. 2+ ) and trivalent metal ions (M 3+ ) does not have to be of only one type; it may include multiple types.

[0027] Nitrate ions (NO3) in the interlayers of layered double hydroxides - These are exchanged with other anions that have a higher affinity for the layered double hydroxide. In this embodiment, a layered double hydroxide containing nitrate ions is referred to as a nitrate-type layered double hydroxide. Nitrate-type layered double hydroxides are obtained from reinforcing steel corroded by salt damage, and chloride ions (Cl) are exchanged. - When adsorbed, nitrate ions NO3 are produced instead. - It releases nitrate ions (NO3). - is iron ion (Fe 2+ It reacts with ) and, according to the following reaction equation (1), produces magnetite (Fe3O4), i.e., black rust, thereby suppressing corrosion of the reinforcing steel. 3Fe+8HNO3→8NO2+Fe3O4+4H2O…(1)

[0028] The layered double hydroxide according to this embodiment is, for example, a divalent metal ion (M 2+ ) is Mg 2+ It is a trivalent metal ion (M 3+ ) is Al 3+ Mg 2+ 1-x Al 3+ x (OH)2(NO3 - ) x / n • mH2O (Mg-Al type) and divalent metal ions (M 2+ ) is Mg 2+ It is a trivalent metal ion (M 3+ ) is Fe 3+ Mg 2+ 1-x Fe 3+ x (OH)2(NO3- ) x / n • mH2O (Mg-Fe type) and divalent metal ions (M 2+ ) is Fe 2+ It is a trivalent metal ion (M 3+ ) is Fe 3+ Fe 2+ 1-x Fe 3+ x (OH)2(NO3 - ) x / n It can be expressed as mH2O (Fe-Fe type). The Mg-Fe type is superior to the Mg-Al type in that it has a higher specific gravity, is easier to separate by sedimentation, and reduces raw material costs.

[0029] Furthermore, the layered double hydroxide according to this embodiment is preferable to have a crystallite size of 20 nm or less, and more preferably 10 nm or less. For example, if the crystallite size of the layered double hydroxide is 20 nm or less, the specific surface area will be 20 m². 2 It can be made to be greater than / g, which can improve adsorption performance.

[0030] Layered double hydroxides are synthesized by mixing an acidic solution containing divalent and trivalent metal ions with an alkaline solution. The specific surface area of ​​the synthesized layered double hydroxide can be increased as the crystallite size decreases. Therefore, a short maturation time after synthesis is desirable, and it is preferable to neutralize the mixture of the acidic and alkaline solutions within at least 120 minutes, preferably within 60 minutes, and even more preferably simultaneously with mixing. Details of the method for synthesizing layered double hydroxides are described in Japanese Patent Application Publication No. 2021-195276.

[0031] (Rust prevention method) Next, based on Figures 1(a) to 1(d), we will explain methods for preventing rust (repair methods) on reinforcing steel embedded inside reinforced concrete (hereinafter referred to as concrete structures) that has been damaged by salt.

[0032] As shown in Figure 1(a), in the case of a concrete structure 10, it is determined through a tapping test by an external worker that the reinforcing bars 20 (the part enclosed by the dashed line) inside the concrete structure 10 have been damaged by salt.

[0033] In this case, as shown in Figure 1(b), the worker breaks off a portion of the concrete structure 10 (the part that has been damaged by salt) to expose the salt-damaged reinforcing bars 20 from the concrete structure 10 (see reference numeral 12 in Figure 1(b)). At this time, the concrete is removed so that the back side of the reinforcing bars 20 is also exposed.

[0034] Next, as shown in Figure 1(c), the worker directly applies the rust inhibitor of this embodiment (a rust inhibitor containing resin and nitrate-type layered double hydroxide) to the reinforcing bars 20 exposed from the concrete structure 10 and to the concrete surface (chipped surface) that was revealed by chipping away at the concrete structure 10.

[0035] After applying the rust inhibitor, the worker waits until a predetermined time has elapsed between the start of hardening and complete hardening of the rust inhibitor. At this predetermined time, as shown in Figure 1(d), the worker covers the chipped area 12 with polymer cement mortar 14 and repairs the cross-section. The predetermined time is approximately one hour after the application of the rust inhibitor, and the rust inhibitor is assumed to be in a sticky (tacky) state.

[0036] Here, if the resin contained in the rust inhibitor is a thermosetting resin, the time (waiting time) from applying the rust inhibitor to covering the chipped area 12 with polymer cement mortar 14 will vary depending on the ambient temperature (temperature around the reinforcing bars 20). If the ambient temperature is high, the waiting time will be shorter, and if the ambient temperature is low, the waiting time will be longer. Therefore, the worker may determine the waiting time based on the ambient temperature and perform the treatment shown in Figure 1(d) once that waiting time has elapsed.

[0037] (Action of nitrate-type layered double hydroxides) As described above, in this embodiment, a rust inhibitor containing a nitric acid-type layered double hydroxide is used. The action of this nitric acid-type layered double hydroxide will be explained based on Figures 2(a) to 2(c).

[0038] Figure 2(a) shows chloride ions (Cl - The diagram shows a state in which a portion of the reinforcing steel 20 has corroded. Normally, the reinforcing steel 20 in concrete structures is covered on the surface by a passive film (Fe2O3) 30, which suppresses the occurrence of oxidation reactions (corrosion). On the other hand, when the chloride ion concentration increases, the passive film disappears as shown by the dashed ellipse A in Figure 2(a), and corrosion occurs.

[0039] When corrosion occurs in a portion of the reinforcing bar 20 as described above, and a rust inhibitor containing nitrate-type layered double hydroxide is applied directly to the reinforcing bar 20, as shown in Figure 2(b), the nitrate-type layered double hydroxide contains chloride ions (Cl - It adsorbs ) and replaces it with nitrate ions (NO3 - ) releases.

[0040] Then, the chemical reaction shown in reaction equation (1) above occurs, and magnetite (Fe3O4), i.e., black rust, is formed in the area indicated by the dashed ellipse A in Figure 2(c). This makes it possible to suppress the corrosion of the reinforcing steel. Here, nitrate ions (NO3 - The conditions for the formation of magnetite (Fe3O4) by rust inhibitors are anaerobic environmental conditions and conditions with as little H2O as possible (dry state). In this embodiment, since the rust inhibitor contains resin as a binder, the surface of the reinforced concrete coated with the rust inhibitor becomes an anaerobic environment. Also, since the resin does not contain water, the surface of the reinforced concrete coated with the rust inhibitor becomes an environment with as little H2O as possible. Thus, in this embodiment, conditions that facilitate the formation of magnetite are ensured in the area covered with the rust inhibitor. In this embodiment, it is preferable to dry the surface of the reinforced concrete (remove moisture) before applying the rust inhibitor.

[0041] (Another action of nitrate-type layered double hydroxides) Furthermore, by using a metal ion with a higher ionization tendency than iron as at least one of the divalent and trivalent metal ions in the nitrate-type layered double hydroxide, the corrosion of reinforcing steel can be further suppressed. Hereinafter, divalent metal ions will be Mg 2+ And trivalent metal ions are Al 3+ This section describes nitrate-type layered double hydroxides.

[0042] The crystallite structure of nitrate-type layered double hydroxide is as shown in Figure 3. As shown in Figure 3, within the crystallite there are trivalent metal ions (Al 3+ ) do not adjacent to each other, maintaining stability. However, Al located at the ends of each crystallite 3+ When crystallites are in close proximity, they become unstable due to mutual repulsion, and each crystallite is more likely to exhibit the properties of Al. In particular, when the crystallite size is small (for example, 10 nm or less), the Al located at the edges of each crystallite becomes unstable. 3+ The crystallites become more likely to come into close proximity, leading to instability, and each crystallite is more likely to exhibit its properties as Al.

[0043] Therefore, when a preservative containing nitrate-type layered double hydroxide is applied to the surface of reinforcing steel, an electric current flows between them due to the difference in ionization tendencies (potential difference) between the Al crystallites of the nitrate-type layered double hydroxide and the reinforcing steel (Fe). As a result, the metal with a higher ionization tendency (lower potential) (Al) is consumed, while the metal with a lower ionization tendency (higher potential) (Fe) is protected from corrosion (cathodic protection).

[0044] Furthermore, Mg located at the ends of each crystallite 2+ The same applies to this: by applying a preservative containing nitrate-type layered double hydroxide to the surface of the reinforcing steel, metals with a high ionization tendency (low potential) (Mg) are consumed, while metals with a low ionization tendency (high potential) (Fe) are protected from rust.

[0045] Also, 3+The hydroxide (Al(OH)3) produced when the compound becomes unstable is an amphoteric hydroxide, and therefore suppresses the formation of red rust (Fe2O3) by chloride ions and promotes the formation of magnetite (Fe3O4), i.e., black rust.

[0046] (Example of experiment) The following describes an example of an experiment that confirmed the action of the rust inhibitor in this embodiment.

[0047] In this experiment, as shown in Figure 4(a), sample 10a was prepared in which a portion of D13 (approximately 13 mm in diameter) deformed reinforcing bar 20a was covered with concrete 40a. The portion of the reinforcing bar not covered with concrete was then immersed once in a 10% NaCl aqueous solution. The chloride ion concentration of concrete 40a was 5 kg / m³. 3 That was the case.

[0048] Next, after drying the reinforcing steel portions that were not covered with concrete, a rust inhibitor containing resin and nitrate-type layered double hydroxide was applied directly to the portions of the reinforcing steel 20a that were not covered with concrete 40a and to the concrete joint surface 41, as shown in Figure 4(b).

[0049] Next, as shown in Figure 4(c), the areas where the rust inhibitor had been applied (reinforcement bars 20a, construction joint surface 41) were covered with polymer cement mortar 14a. After that, the material was cured in a constant temperature chamber at 23°C and 60% humidity for two and a half years.

[0050] Subsequently, as shown in Figure 4(d), the reinforcing bar 20a was chipped away, and the crystalline compounds formed in the reinforcing bar portion coated with rust inhibitor were estimated using an X-ray diffraction apparatus.

[0051] Figure 5 shows the X-ray diffraction results obtained using an X-ray diffractometer. In Figure 5, the horizontal axis represents the diffraction angle 2θ (deg), and the vertical axis represents the X-ray intensity. From Figure 5, it was found that in addition to Fe2O3, FeO, and Fe, magnetite (Fe3O4) was present in the reinforcing steel portion coated with the rust inhibitor. In other words, this experiment proved that the reaction shown in reaction equation (1) above occurred in the reinforcing steel portion coated with the rust inhibitor.

[0052] As described in detail above, according to this embodiment, when rust-preventing reinforcing bars that have salt (chloride ions) attached to them, a rust inhibitor containing resin and a nitrate-type layered double hydroxide is directly applied. As a result, the nitrate-type layered double hydroxide applied to the reinforcing bars adsorbs chloride ions and releases nitrate ions, so that magnetite (Fe3O4), i.e., black rust, is formed on the surface of the reinforcing bars as shown in reaction equation (1) above. As a result, red rust does not form on top of the black rust, and the occurrence of corrosion in the reinforcing bars can be effectively suppressed. Here, conventionally known rust inhibitors include aqueous solutions containing nitrite ions. Such aqueous solutions containing nitrite ions pose a risk of exposure to human health and environmental burden. On the other hand, in the case of the rust inhibitor of this embodiment, although it contains nitrate ions, the nitrate ions are fixed in the layered double hydroxide (solid) before being applied to the reinforcing bars. As a result, nitrate ions are released to the outside of the layered double hydroxide only in the presence of chloride ions, so there is almost no risk of exposure to human health or environmental burden.

[0053] Furthermore, in this embodiment, since the rust inhibitor contains resin, the area to which the rust inhibitor is applied can be made an anaerobic environment with minimal H2O. This allows the reaction of reaction formula (1) described above to be further accelerated.

[0054] Furthermore, conventionally known rust inhibitors sometimes use cement-based materials as binders. However, with rust inhibitors containing such cement-based materials, it is not possible to perform cross-sectional repair treatment using polymer cement mortar (see Figure 1(d)) unless the material is cured for, for example, 16 hours or more after application. This is because polymer cement mortar cannot be applied when the cement-based material is semi-dry. In contrast, by using resin as a binder, as in this embodiment, it becomes possible to apply polymer cement mortar even when the resin is semi-dry (from the time the rust inhibitor begins to harden until it is completely hardened). Therefore, after applying the rust inhibitor, it becomes possible to perform cross-sectional repair treatment using polymer cement mortar (see Figure 1(d)) in a short time (for example, about 1 hour). This makes it possible to perform rust prevention work efficiently and in a short time.

[0055] Furthermore, in this embodiment, by making at least one of the divalent and trivalent metals of the layered double hydroxide a metal with a higher ionization tendency than iron, the occurrence of corrosion of the reinforcing steel can be more effectively suppressed by the cathodic protection function of the metal with a higher ionization tendency than iron.

[0056] Furthermore, in this embodiment, by setting the crystallite size of the layered double hydroxide to 10 nm or less, the effect of metals with a higher ionization tendency than iron located at the edges of the crystallites can be made more pronounced. The inventors have confirmed that when using a layered double hydroxide with a crystallite size of approximately 9.1 to 9.2 nm (measured using X-ray diffraction results and Scherrer's formula), the occurrence of rebar corrosion is reduced compared to the conventional case (crystallite size of approximately 23 to 36 nm).

[0057] In the above embodiment, we have described a case in which a rust inhibitor containing a resin and a nitrate-type layered double hydroxide is applied to reinforcing bars for rust prevention treatment. However, the invention is not limited to this, and rust inhibitors may also be applied to steel materials other than reinforcing bars for rust prevention treatment.

[0058] The embodiments described above are preferred examples of the present invention. However, the invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0059] 10 Concrete structures 20 Reinforcing bars (steel materials) 14 Polymer cement mortar

Claims

1. For steel materials with salt adhered thereto, a resin and a layered double hydroxide represented by the chemical formula M 2+ 1-x M 3+ x (OH) 2 (NO 3 - ) x / n ·mH 2 O (where M 2+ represents a divalent metal, M 3+ represents a trivalent metal, 0 < x < 1, m is a number greater than 0, and n is a natural number), and a rust inhibitor having the same are directly applied; A method for preventing rust on steel, comprising the step of covering the steel with a concrete material during the period from when the rust inhibitor begins to harden until it is completely hardened.

2. The resin contained in the aforementioned rust inhibitor is a thermosetting resin. The method for preventing rust on steel according to claim 1, wherein the time from applying the rust inhibitor to the steel to covering the steel with the concrete material varies depending on the ambient temperature of the steel.

3. The process includes a step of breaking up a portion of the concrete structure in which the steel material is embedded, thereby exposing the steel material to which salt has adhered from the concrete structure. In the step of directly applying the rust inhibitor, the rust inhibitor is directly applied to the steel material exposed from the concrete structure and to the concrete surface exposed by chipping away at the concrete structure. The method for preventing rust on steel materials according to claim 1 or 2, wherein in the covering step, the portion of the concrete structure that has been chipped is filled with the concrete material.

4. The method for preventing rust on steel materials according to claim 1, wherein the resin is one of an epoxy resin, an acrylic resin, or a urethane resin.

5. The method for preventing rust on steel according to claim 1, wherein the layered double hydroxide adsorbs chloride ions and forms black rust on the surface of the steel.

6. The method for preventing rust on steel according to claim 1, wherein at least one of the divalent metal and the trivalent metal of the layered double hydroxide has a greater ionization tendency than iron.

7. The method for preventing rust on steel according to claim 6, wherein at least one of the divalent metal and the trivalent metal of the layered double hydroxide prevents rust on the steel by cathodic protection.

8. The method for preventing rust on steel according to claim 6 or 7, wherein the crystallite size of the layered double hydroxide is 10 nm or less.

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