Methods for repairing concrete structures

Abstract

In order to improve oxidation resistance characteristics during processing and assembly of a reinforcing bar, a method for processing a reinforcing bar according to the present invention includes: a step for applying a layered double hydroxide represented by chemical formula: M2+ 1-xM3+ x (OH)2(NO3 -) x / n•mH2O, (wherein M2+ represents a bivalent metal; M3+ represents a trivalent metal; and n is a natural number), to at least a processed part of the reinforcing bar; and a step for making it possible to identify the part to which the layered double hydroxide is applied.

Description

Methods for processing rebars, assembling rebars, and repairing concrete structures

[0001] The present invention relates to a method for processing reinforcing bars, a method for assembling reinforcing bars, and a method for repairing concrete structures.

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

[0003] However, there are problems with concrete, such as its durability being reduced due to carbon dioxide neutralization, and when cracks appear on the surface of the concrete, oxygen and moisture can penetrate through the cracks, causing rust on the reinforcing bars.

[0004] For this reason, it has been proposed to improve the carbonation resistance of concrete and the oxidation resistance of reinforcing bars by producing ready-mix concrete using nitrogen-dissolved water in which the oxygen and carbon dioxide dissolved in the water used to produce the concrete are replaced with nitrogen (see, for example, Patent Document 1).

[0005] International Publication No. 2018 / 189915

[0006] Patent Document 1 does not take into consideration the oxidation resistance of reinforcing bars during processing or assembly. Furthermore, Patent Document 1 found that if oxygen or carbon dioxide enters the surface of reinforced concrete after manufacture, the carbonation resistance and oxidation resistance would inevitably deteriorate, and it was also not possible to accurately predict the degree of corrosion of reinforced concrete.

[0007] Therefore, an object of the present invention is to provide a method for processing reinforcing bars and a method for assembling reinforcing bars that can improve the oxidation resistance of reinforcing bars during processing and assembly. Another object of the present invention is to provide a method for repairing concrete structures that can efficiently suppress corrosion of reinforced concrete.

[0008] The method for processing reinforcing bars of the present invention is 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n Layered double hydroxide (M 2+ is a divalent metal, M 3+ The method for assembling a reinforcing bar of the present invention includes a step of applying a layered double hydroxide having the chemical formula M to at least the processed portion of the reinforcing bar, and a step of making the portion to which the layered double hydroxide is applied identifiable. 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n Layered double hydroxide (M 2+ is a divalent metal, M 3+ The method for repairing a concrete structure of the present invention includes a step of applying a layered double hydroxide having the chemical formula M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n Layered double hydroxide (M 2+ is a divalent metal, M 3+ represents a trivalent metal, and n is a natural number) before or after pouring concrete of a concrete structure; placing a first concrete specimen containing the layered double hydroxide and having the same components as the concrete structure but smaller in size near the concrete structure; and applying the layered double hydroxide to the concrete structure based on the condition of the first concrete specimen a predetermined time after the concrete structure is constructed.

[0009] According to the reinforcing bar processing method of the present invention, the chemical formula is M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / nSince the layered double hydroxide represented by mH2O is applied to at least the processed portion of the reinforcing bar, the oxidation resistance of the reinforcing bar during processing can be improved. In addition, by making the portion coated with the layered double hydroxide identifiable, the portion coated with the layered double hydroxide can be visually recognized. According to the reinforcing bar assembling method of the present invention, 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n The layered double hydroxide represented by mHO is applied to the bonded portion between the first and second reinforcing bars, thereby improving the oxidation resistance of the reinforcing bars during assembly. Furthermore, by making the area to which the layered double hydroxide is applied identifiable, the area to which the layered double hydroxide is applied can be visually confirmed. According to the concrete structure repair method of the present invention, the layered double hydroxide is applied to the concrete structure based on the condition of the first specimen concrete, thereby enabling efficient repair of the concrete structure.

[0010] 6(a) is an outline diagram of a coating agent application device of a first embodiment; FIG. 6(b) is a block diagram of a coating agent application device of a first embodiment; FIG. 6(c) is a block diagram of a coating agent application device of a first embodiment; FIG. 6(a) is a block diagram of a coating agent application device of a first embodiment; FIG. 6(c ...

[0011] Hereinafter, a method for processing reinforcing bars, a method for assembling reinforcing bars, and a method for repairing a concrete structure according to an embodiment will be described.

[0012] (First embodiment) (Regarding coating agent) First, the coating agent used in this embodiment will be described. The coating agent of this embodiment contains a resin that functions as a binder and a layered double hydroxide. Alternatively, the coating agent may be prepared by mixing a layered double hydroxide with a paint containing a resin, or by mixing a layered double hydroxide with a paint that does not contain a resin.

[0013] In either case, the paint contains a color pigment so that the layered double hydroxide can be easily identified. Pigments can fade due to ultraviolet rays and the like, and in CMYK, it is said that yellow, magenta, cyan, and black fade most easily in this order. However, in this first embodiment, a coating agent is intended to be applied to reinforcing bars installed inside reinforced concrete. Therefore, reinforcing bars covered with concrete are less affected by ultraviolet rays. For this reason, in this first embodiment, yellow or magenta (reddish purple) can be used as a pigment, making it easier to distinguish from the color of the reinforcing bars.

[0014] (Resin) The resin may be a curable liquid resin that can coat the surface of concrete or reinforcing bars and 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 alone or in combination of two or more. The resin may be a one-component resin or a two-component resin.

[0015] (Epoxy Resin) Examples of epoxy resins that can be used include bisphenol A epoxy resins, halogenated bisphenol A epoxy resins, bisphenol F epoxy resins, novolac epoxy resins, and cresol novolac epoxy resins.

[0016] Examples of bisphenol A epoxy resins include condensation polymers of bisphenol A 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. These epoxy resins can be used alone or in combination of two or more.

[0017] A reactive diluent can also be added to and blended with the epoxy resin. Such a reactive diluent is effective in reducing the viscosity of the composition. Examples of such a reactive diluent include compounds having one epoxy group in the molecule, such as phenyl glycidyl ether, butyl glycidyl ether, allyl glycidyl ether, styrene oxide, and octylene oxide. The amount of such a reactive diluent can be preferably 45% by weight or less, and more preferably 25% by weight or less, based on the base resin.

[0018] Furthermore, epoxy resins can also be blended with additives that do not contain epoxy groups but can react with curing agent components (such as amine compounds). Examples of such compounds include isocyanates such as hexamethylene diisocyanate and tolylene diisocyanate, as well as α,β-unsaturated carbonyl compounds that undergo a Michael addition reaction with amine compounds, such as acrylic esters and acrylamide derivatives. Acrylic esters are effective in improving low-temperature curing properties, while acrylamide derivatives are effective in improving thixotropy or adhesive properties. Such additives can be blended in amounts of preferably 30% by weight or less, more preferably 20% by weight or less, based on the base resin.

[0019] The epoxy resin may also contain other components such as plasticizers, dyes, organic pigments, inorganic fillers, polymeric compounds, antioxidants, ultraviolet absorbers, coupling agents, and surfactants.

[0020] (Acrylic Resin) Examples of the acrylic resin include polymers of acrylic monomers and copolymers of acrylic monomers with other monomers. Examples of the acrylic monomer include C1-10 alkyl (meth)acrylate esters 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 (meth)acrylate esters such as cyclohexyl (meth)acrylate, aryl (meth)acrylate esters such as phenyl (meth)acrylate, aralkyl (meth)acrylate esters such as benzyl (meth)acrylate, and hydroxy C2-6 esters such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate. Examples of the alkylamino-alkyl (meth)acrylate include alkyl(meth)acrylates such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and diethylaminopropyl (meth)acrylate; (meth)acrylamides or derivatives thereof 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.

[0021] Examples of monomers copolymerizable with the acrylic monomer include aromatic vinyl monomers such as styrene, α-methylstyrene, p-t-butylstyrene, and vinyltoluene, fatty acid vinyl ester monomers such as vinyl propionate, esters of 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 alone or in combination of two or more.

[0022] (Urethane Resin) As the urethane resin, for example, a urethane prepolymer having a free isocyanate group obtained by reacting a polyol with a polyisocyanate can be used.

[0023] As the polyol, polyether polyol, polyolefin polyol, or the like can be used.

[0024] Suitable examples of polyether polyols include polyalkylene polyols having 2 to 4 hydroxyl groups (active hydrogen groups) in the molecule, which are obtained by addition polymerization of a polyol having 2 to 8 carbon atoms and having two or more, preferably 2 to 6, hydroxyl groups, such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, glycerin, hexanediol, hexanetriol, glycerin, trimethylolpropane, or pentaerythritol, with an alkylene oxide having preferably 2 to 8 carbon atoms, such as ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran, in the presence of an alkali catalyst.

[0025] Suitable polyolefin polyols include polydiene polyols having 2 to 4 hydroxyl groups per molecule, which are obtained by addition polymerization of alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran with diene compounds such as butadiene and isoprene. Suitable polyisocyanates are compounds having two or more, preferably two to three, isocyanate groups per molecule.

[0026] Specific examples of polyisocyanates 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, and isophorone diisocyanate; biuret polyisocyanate compounds such as Sumidur N (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.); Desmodur IL, HL (trade name, manufactured by Bayer A.G.), and Coronate E.H. (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.) and other polyisocyanate compounds having an isocyanate ring; and adduct polyisocyanate compounds such as Sumidur L (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.) and Coronate HL (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.) These polyisocyanates can be used alone or as a mixture of two or more.

[0027] (Layered double hydroxide) Layered double hydroxide is a compound having the chemical formula M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n mH2O, where M 2+ is 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 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. 2+ ) for example, Mg 2+ , Fe 2+ , Zn 2+ , Li 2+ , Ni 2+ , Co 2+ , Cu 2+ In addition, trivalent metal ions (M3+ ) is, for example, Al 3+ , Fe 3+ , Cr 3+ , Mn 3+ The divalent metal ions (M 2+ ) and trivalent metal ions (M 3+ ) does not have to be of one type, and may include multiple types.

[0028] Nitrate ions NO3 between the layers of layered double hydroxide - Nitrate ions are exchanged with other anions that have a higher affinity with the layered double hydroxide. The layered double hydroxide containing nitrate ions as in this embodiment is called a nitric acid type layered double hydroxide. Nitrate type layered double hydroxides are formed by exchanging chloride ions (Cl) from reinforcing bars corroded by salt damage. - ) and chloride ions (Cl) that have entered from the outside and attached to the rebar. - ) and instead nitrate ions NO3 - The released nitrate ions NO3 - is iron ion (Fe 2+ ) to produce magnetite (Fe3O4), i.e., black rust, according to the following reaction formula (1), thereby inhibiting corrosion of reinforcing bars: 3Fe + 8HNO3 → 8NO2 + Fe3O4 + 4H2O (1)

[0029] The layered double hydroxide according to this embodiment may contain, for example, a divalent metal ion (M 2+ ) is Mg 2+ and trivalent metal ions (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+ and trivalent metal ions (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+ and trivalent metal ions (M 3+ ) is Fe 3+ Fe 2+ 1-x Fe 3+ x (OH)2(NO3 - ) x / n ・mH2O (Fe-Fe type). The Mg-Fe type is superior to the Mg-Al type in that it has a high specific gravity, making it easy to separate by sedimentation, and it can reduce raw material costs.

[0030] Furthermore, the layered double hydroxide according to this embodiment preferably has a crystallite size of 20 nm or less, 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 can be increased to 20 m. 2 / g or more, and the adsorption performance can be improved.

[0031] The layered double hydroxide is synthesized by mixing an acidic solution containing divalent metal ions and trivalent metal ions with an alkaline solution. The smaller the crystallite size of the layered double hydroxide synthesized here, the larger its specific surface area can be. Therefore, the shorter the aging time after synthesis, the better, and after mixing the acidic solution and the alkaline solution, it is better to neutralize them within at least 120 minutes, preferably within 60 minutes, and more preferably simultaneously with mixing. Details of the method for synthesizing layered double hydroxides are described in JP 2021-195276 A.

[0032] (Method of Processing Reinforcing Bars) Reinforcing bars are manufactured by using scrap iron or the like as raw materials, melting them in an electric furnace, transferring them to a ladle for refining, forming them into a certain shape in a continuous casting machine, rolling them in a rolling mill, and cutting them to a predetermined length. In this first embodiment, a coating agent containing a nitric acid-type layered oxide is used to perform a rust prevention treatment on reinforcing bars R that have been cut (processed) to a predetermined length and cooled.

[0033] (Coating agent application device) Fig. 1 is a diagram showing a schematic diagram of a coating agent application device 1 of the first embodiment, and Fig. 2 is a block diagram of the coating agent application device 1 of the first embodiment. The coating agent application device 1 of the first embodiment will be described below with reference to Figs. 1 and 2.

[0034] The coating agent application device 1 of the first embodiment is an apparatus for applying a coating agent to reinforcing bars R. The coating agent application device 1 includes a conveying device 2 for conveying the reinforcing bars R in the direction of the arrow in Figure 1, an application device 4 for applying a coating agent stored in a tank 3 to the reinforcing bars, a first memory 5, and a first control device 6.

[0035] The conveying device 2 has a plurality of rollers spaced apart in the conveying direction, and a motor (not shown) rotates the rollers to convey the reinforcing bars R in the direction of the arrow in Fig. 1. Although Fig. 1 shows two reinforcing bars R, this is not limiting, and a plurality of reinforcing bars R may be arranged in a direction perpendicular to the plane of the drawing.

[0036] The tank 3 stores the coating agent and can be made of a metal material or a resin material. If a stirring mechanism is provided in the tank 3, the nitric acid type layered oxide can be uniformly distributed in the paint, thereby reducing the amount of the nitric acid type layered oxide used.

[0037] The coating device 4 has a nozzle, and in this first embodiment, it has a nozzle 4a that sprays the coating agent onto the reinforcing bar R from above the reinforcing bar R, and a nozzle 4b that sprays the coating agent onto the reinforcing bar R from below the reinforcing bar R.

[0038] Nozzle 4a is tilted so that the coating agent can be sprayed onto one end of the reinforcing bar R (end Re of the reinforcing bar R). On the other hand, nozzle 4b is tilted so that the coating agent can be sprayed onto the other end of the reinforcing bar R (tip Rt of the reinforcing bar R). By tilting nozzle 4a and nozzle 4b in different directions, the coating device 4 can spray the coating agent onto both ends of the reinforcing bar R in addition to the surface of the reinforcing bar R.

[0039] Since nozzle 4b sprays the coating agent onto the reinforcing bars R against gravity, it is preferable that the application pressure be greater than that of nozzle 4a and that the application amount be greater than that of nozzle 4a. The nozzles 4a and 4b are controlled by a first control device 6, which will be described later. The number of nozzles 4a and 4b can be set arbitrarily, and for example, a plurality of nozzles 4a and 4b may be arranged in the direction perpendicular to the plane of the drawing.

[0040] Figure 3 is a view of the coating agent application device 1 as seen from the arrow A in Figure 1. As shown in Figure 3, the coating agent application device 1 of the first embodiment is provided with five nozzles 4a and five nozzles 4b along the Y direction. Also, as shown in Figure 3, 12 reinforcing bars R are transported by a transport device 2 in the direction perpendicular to the plane of the page.

[0041] It is preferable that the nozzles 4a and 4b are arranged offset in the direction perpendicular to the plane of the paper in Fig. 3 (the conveying direction). This is because if the nozzles 4a and 4b were to face each other in the direction perpendicular to the plane of the paper, there is a risk that the spray pressures of the two nozzles would cancel each other out. It is also preferable that the reinforcing bars R are fed into the coating agent application device 1 without being bundled. This is because there is a possibility that the coating agent will not be applied to the binding wires that bundle the reinforcing bars R. In particular, if the reinforcing bars R are bundled in the vertical direction, there is a high likelihood that portions of the reinforcing bars R will not be coated with the coating agent.

[0042] The first memory 5 is a non-volatile memory (for example, a flash memory), and in the first embodiment, stores a program for driving the transport device 2, a program for driving the coating device 4, and the like.

[0043] The first control device 6 includes a CPU and controls the entire coating agent application device 1, including the conveying speed of the conveying device 2 and the application pressure and application amount of the application device 4.

[0044] According to the coating agent application device 1 of the first embodiment configured as described above, the coating agent is applied after processing, which is the manufacturing stage of the reinforcing bar R, so that it is possible to perform rust prevention treatment on the reinforcing bar R. More specifically, when the reinforcing bar R is used as reinforced concrete, chloride ions (Cl -) enters the reinforcing bar R, the nitrate-type layered double hydroxide contained in the coating agent will - ) and can prevent rusting of the reinforcing bars R. This allows the life of the reinforced concrete to be extended, and the frequency of chipping the reinforced concrete and applying the coating agent to the reinforcing bars R can be reduced.

[0045] Furthermore, with the coating agent application device 1 of the first embodiment, yellow or magenta (reddish purple) is used as the pigment, making it easier to see the areas coated with the coating agent containing the nitric acid-type layered oxide. If the rebar R coated with the coating agent is cut again to adjust its length, the end face of the cut rebar R will not be coated with the pigment. However, the worker can visually recognize that the coating agent must be applied again to this end face. When reapplying the coating agent to the end face of the rebar R, the worker can apply it by hand using a roller, trowel, or brush, or by spraying, without using the coating agent application device 1.

[0046] Furthermore, when bending a reinforcing bar R to which a coating agent has been applied, cracks or peeling may occur in the coating agent at the bent portion of the reinforcing bar R. For this reason, it is desirable to reapply the coating agent to the bent portion even after bending.

[0047] In the first embodiment described above, the coating agent is applied to the reinforcing bar R by the coating agent application device 1, but the coating agent may be applied by immersing the reinforcing bar R in a container filled with the coating agent.

[0048] Second Embodiment Hereinafter, a second embodiment will be described with reference to Fig. 4. The same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted or simplified. In the second embodiment, the description will be continued using an example in which a plurality of reinforcing bars R are assembled.

[0049] 4 is a diagram showing a unit reinforcing bar 10. The unit reinforcing bar 10 has main reinforcements 11 made of reinforcing bars R that act on the bending moment of reinforced concrete, stirrup reinforcements 12 made of reinforcing bars R that fix the relative positions of the main reinforcements 11, web reinforcements 13 made of reinforcing bars R that prevent deformation of the stirrup reinforcements 12, and binding wires 14 made of metal wire that fix the contact points between the reinforcing bars R.

[0050] The stirrup reinforcement 12 has a hook portion that engages with the upper main reinforcement 11 and a bent portion that engages with the lower main reinforcement 11. The number of stirrup reinforcement 12 and the number of abdominal reinforcement 13 can be set as desired.

[0051] Because the binding wires 14 are made of metal, there is a risk that rust will occur if oxygen, moisture, or the like penetrates through cracks in the concrete, which could ultimately cause the unit reinforcing bars 10 to rust as well. Therefore, in the second embodiment, the binding wires 14 are coated with the coating material of the first embodiment after the unit reinforcing bars 10 are assembled and before concrete is poured using a formwork (not shown). The coating material can be applied to the binding wires 14 by hand using a roller, trowel, or brush, or by spraying. Furthermore, in addition to the binding wires 14, it is preferable to apply the coating material to the contact points (joints) between the reinforcing bars R. Furthermore, if there are any portions of the unit reinforcing bars 10 that have already corroded due to salt damage or the like, it is preferable to apply the coating material to these corroded portions as well.

[0052] Here, by using a resin as a primer for the coating agent, concrete can be poured even when the resin is semi-dry (between the time when the coating agent begins to harden and the time when it is completely hardened). Therefore, concrete can be poured within the time it takes to assemble the formwork (not shown), so the application of the coating agent to the binding wires 14 does not extend the concrete pouring process. Furthermore, if the assembly of the formwork (not shown) and the application of the coating agent to the binding wires 14 are carried out in parallel, concrete can be poured more efficiently.

[0053] As described above, according to the second embodiment, by applying the coating agent to the binding wire 14, the binding wire 14 can be treated to prevent rust before the concrete is poured, thereby extending the life of the reinforced concrete and reducing the frequency with which the reinforced concrete needs to be chipped and the coating agent applied to the reinforcing bars R.

[0054] (Third Embodiment) A third embodiment will be described below using Figure 5. The same components as those in the first and second embodiments are designated by the same reference numerals, and their description will be omitted or simplified. In the third embodiment, a small-sized concrete specimen 25 having the same concrete components as the concrete structure 20 is placed on or near the concrete structure 20. It is preferable that concrete produced in the same lot or around the same time be used for the concrete specimen 25 and the concrete structure 20 in a concrete plant that produces concrete. The concrete structure 20 can be widely used in various buildings such as commercial facilities, sports facilities, and logistics warehouses, as well as dams.

[0055] As shown in Figure 5, a concrete specimen 25 is provided on the roof of a concrete structure 20. In Figure 5, one concrete specimen 25 is provided, but multiple concrete specimens 25 may be provided, for example, depending on the direction. The concrete specimens 25 may also be provided at different heights, such as on the ground and on the roof. In order to infer the neutralization of the concrete structure 20, it is preferable that the concrete specimens 25 be provided in the same environment, and it is preferable that they be provided in a place that is open to the outside air, such as outdoors or on a balcony.

[0056] In this third embodiment, the concrete structure 20 contains the nitric acid type layered double hydroxide described in the first embodiment. However, in order to reduce the manufacturing cost of the concrete structure 20, it is preferable that the concrete structure 20 does not contain resin. The nitric acid type layered double hydroxide may be added to the concrete before it is poured, or the nitric acid type layered double hydroxide may be sprayed onto the surface of the poured concrete, for example, by a spray.

[0057] When adding nitric acid type layered double hydroxide to concrete before it is poured, the concrete can be mixed with the nitric acid type layered double hydroxide, for example, using a mixer truck. In this case, the nitric acid type layered double hydroxide is mixed throughout the concrete structure 20, so that the nitric acid type layered double hydroxide adsorbs carbon dioxide near the surface of the concrete structure 20, thereby suppressing neutralization of the concrete structure 20. Even if carbon dioxide gets inside the concrete structure 20, the nitric acid type layered double hydroxide inside the concrete structure 20 adsorbs this carbon dioxide, thereby suppressing neutralization of the concrete structure 20.

[0058] On the other hand, when applying the nitric acid type layered double hydroxide to the surface side of the poured concrete, a spray, roller, trowel, brush, etc. can be used. When applying a spray tile finish to the surface of the concrete structure 20, it is preferable to apply the nitric acid type layered double hydroxide as a primer.

[0059] When tiles are attached to the surface of the concrete structure 20, the attached tiles may be masked and the nitric acid layered double hydroxide may be applied to the joints, for example, using a brush. When the nitric acid layered double hydroxide is applied to the surface side of the concrete after pouring, the amount of nitric acid layered double hydroxide used can be reduced compared to when the nitric acid layered double hydroxide is incorporated into the concrete before pouring, making it possible to construct the concrete structure 20 at low cost. Furthermore, the nitric acid layered double hydroxide adsorbs carbon dioxide near the surface of the concrete structure 20, thereby suppressing neutralization of the concrete structure 20.

[0060] Reinforcing bars R are provided inside the concrete structure 20, and it is preferable to apply a coating agent containing a nitric acid-type layered double hydroxide to these reinforcing bars R, as described in the first or second embodiment.

[0061] The concrete specimen 25 may have the same composition as the concrete structure 20. In other words, when the concrete structure 20 is to contain the nitric acid type layered double hydroxide throughout, the concrete specimen 25 may contain the nitric acid type layered double hydroxide throughout.

[0062] Furthermore, if the concrete structure 20 has been given a sprayed tile finish, the surface of the concrete specimen 25 can also be given a sprayed tile finish using nitric acid layered double hydroxide. Furthermore, if tiles are to be attached to the surface of the concrete structure 20, tiles can also be attached to the surface of the concrete specimen 25, and nitric acid layered double hydroxide can be applied to the joints. If reinforcing bars R coated with nitric acid layered double hydroxide are also provided inside the concrete specimen 25, the rust prevention state of the reinforcing bars R inside the concrete structure 20 can be predicted from the rust prevention state of the reinforcing bars R when the concrete specimen 25 is cut out.

[0063] In addition, it is preferable to prepare a concrete specimen 25 that has the same concrete components but does not contain nitric acid-type LDH. By comparing a specimen containing nitric acid-type LDH with a specimen not containing nitric acid-type LDH, it is possible to clarify the carbonation-inhibiting effect of nitric acid-type LDH and the rust-preventing effect on steel materials such as reinforcing bars. It is also preferable to paint a different pigment on the reinforcing bars R of specimens that do not contain nitric acid-type LDH to make them distinguishable from the reinforcing bars R of specimens that contain nitric acid-type LDH.

[0064] For example, several years after the concrete structure 20 is constructed, salt damage to the reinforcing bars R within the concrete structure 20 and carbonation of the concrete are predicted or estimated by checking for cracks on the surface of the concrete specimen 25 and by conducting a hammering test. If there is a possibility of salt damage to the reinforcing bars R within the concrete structure 20 or carbonation of the concrete, a portion of the concrete specimen 25 can be cut out to predict or estimate the salt damage to the reinforcing bars R within the concrete structure 20 and the carbonation of the concrete. In this case, if multiple concrete specimens 25 are arranged, it is sufficient to cut out a concrete specimen 25 that has a possibility of salt damage to the reinforcing bars R within the concrete structure 20 or carbonation of the concrete.

[0065] Alternatively, after several years have passed since the concrete structure 20 was constructed, portions of all the concrete specimens 25 or a plurality of the concrete specimens 25 arranged at intervals may be cut out to predict or estimate salt damage to the reinforcing bars R within the concrete structure 20 and the state of carbonation of the concrete. By cutting out portions of all or a plurality of the concrete specimens 25 arranged at intervals, it is possible to predict or estimate the tendency of areas prone to salt damage and carbonation. In this case, if images of the surface and the interior of the concrete structure 20 are acquired and compiled into a database to be used as training data, it becomes possible to predict salt damage to the reinforcing bars R and the state of carbonation of the concrete using artificial intelligence.

[0066] Furthermore, a portion of the cut concrete or reinforcing bar R may be collected and analyzed for elements attached to the concrete or reinforcing bar R using an electron probe micro analyzer (EPMA) or X-ray diffraction (XRD). In the case of EPMA analysis, it is preferable to obtain images using a reflected electron beam or a secondary electron beam in addition to the above-mentioned images and use them as training data.

[0067] Furthermore, if images of the surface and interior of test specimens containing nitric acid-type LDH are obtained, as well as images of the surface and interior of test specimens not containing nitric acid-type LDH, and these images are compiled into a database, it will be possible to clarify the rust-preventing and carbonation-suppressing effects of nitric acid-type LDH and to accurately optimize the content of nitric acid-type LDH. In this case, too, it is preferable to perform EPMA analysis or XRD analysis to obtain images using a backscattered electron beam or a secondary electron beam and use these as training data.

[0068] If salt damage to the reinforcing bars R of the concrete specimen 25 or neutralization of the concrete is confirmed, the nitric acid-type layered double hydroxide can be applied to the surface of the concrete structure 20 according to the location of the concrete specimen 25. Similarly, the nitric acid-type layered double hydroxide can be applied to a portion of the concrete specimen 25 that has been cut out.

[0069] Figure 6 is an enlarged view of the concrete specimen 25, with Figure 6(a) being the concrete specimen 25 before cutting, Figure 6(b) being the concrete specimen 25 after the first cutting, and Figure 6(c) being the concrete specimen 25 after the second cutting. The dotted line in Figure 6 is an imaginary line indicating the portion where the mth cutting will be performed (m is a natural number).

[0070] As shown in Figure 6(a), in this third embodiment, the concrete specimen 25 can be divided into eight blocks (D11 to D42) corresponding to seven cuttings. If the concrete specimen 25 is cut out every five years, for example, it is possible to check the state of concrete neutralization and salt damage to reinforcing bars R over a 40-year period. The size of the concrete specimen 25 may be set according to the service life of the concrete structure 20, or multiple concrete specimens 25 may be placed adjacent to each other.

[0071] The size of one block can be set to, for example, several centimeters to several tens of centimeters, but is not limited to this. In the third embodiment, the shape of the concrete specimen 25 is a rectangular parallelepiped to match the shape of the concrete structure 20, but the shape can be set arbitrarily.

[0072] Figure 6(b) shows the state in which block D11 has disappeared after the first cutting. Nitric acid-type layered double hydroxide is applied to the concrete specimen 25 after the first cutting, depending on the position from the surface of the concrete structure 20 to which the nitric acid-type layered double hydroxide was applied. For example, suppose that nitric acid-type layered double hydroxide is applied to the front and right side of the upper right end portion of the concrete structure 20 shown in Figure 5. In this case, the concrete specimen 25 provided corresponding to the upper right end portion of the concrete structure 20 has nitric acid-type layered double hydroxide applied to the front and right side. This allows the concrete specimen 25 and the concrete structure 20 corresponding to this concrete specimen 25 to be maintained in the same state.

[0073] Note that the top surface of block D21, which is shown with diagonal lines and exposed to the atmosphere due to the first cutting, and the left side surface of block D12, which is in a blind spot, are in a different situation from the concrete structure 20 in which no cutting is performed. For this reason, in this third embodiment, it is preferable not to use the surfaces exposed by cutting as the subject of evaluation for salt damage to the reinforcing bars R or carbonation of the concrete. For this reason, in this third embodiment, the front and back surfaces of the concrete specimen 25 may be used as the subject of evaluation for salt damage to the reinforcing bars R and carbonation of the concrete. Note that if a nitric acid-type layered double hydroxide is applied to, for example, the top surface of the concrete structure 20, it is preferable to apply a nitric acid-type layered double hydroxide to the top surface of block D21.

[0074] If salt damage to the reinforcing bars R of the concrete specimen 25 or neutralization of the concrete cannot be confirmed, the nitric acid-type layered double hydroxide is not applied to the surface of the cut-out concrete specimen 25 or the concrete structure 20 corresponding to this cut-out concrete specimen 25. This allows the concrete specimen 25 and the concrete structure 20 corresponding to this concrete specimen 25 to be kept in the same condition.

[0075] 6(c) shows the state in which block D12 has disappeared after the second cutting. After the second cutting, nitric acid-type layered double hydroxide is applied to the concrete specimen 25 in accordance with the position from the surface of the concrete structure 20 where the nitric acid-type layered double hydroxide was applied.

[0076] The top surface of block D21, shown with diagonal lines and exposed to the atmosphere after the first cutting, and the top surface of block D22, shown with diagonal lines and exposed to the atmosphere after the second cutting, are in a different situation from the concrete structure 20 in which no cutting has been performed. For this reason, as described above, the surface side exposed by cutting is not subject to evaluation of salt damage to the reinforcing bars R or neutralization of the concrete. If nitrate-type layered double hydroxide is applied to, for example, the top surface of the concrete structure 20, it is preferable to apply nitrate-type layered double hydroxide to the top surfaces of blocks D21 and D22. The second cutting may be block D21 instead of block D12.

[0077] Furthermore, if there are voids on the surface of the concrete structure 20, the nitric acid type layered double hydroxide may be injected through these voids into the interior of the concrete structure 20 using a special tool. Similarly, if there are voids on the surface of the concrete specimen 25, the nitric acid type layered double hydroxide may be injected through these voids into the interior of the concrete specimen 25 using a special tool.

[0078] When constructing the concrete structure 20 using a construction 3D printer, the nitric acid type layered double hydroxide may be mixed into the concrete before it hardens, or the nitric acid type layered double hydroxide may be applied to the surface of the concrete after it hardens.

[0079] The above-described embodiment is a preferred example of the present invention. However, the present invention is not limited to this, and various modifications are possible within the scope of the gist of the present invention. For example, the surfaces of the concrete structure 20 and the concrete specimen 25 may be inspected by a robot equipped with an imaging device instead of a worker. Furthermore, image data of the surfaces of the concrete structure 20 and the concrete specimen 25 photographed by this robot may be sent to a host computer, for example, by wireless communication.

[0080] The host computer may determine whether or not the application of the nitrate-type layered double hydroxide is necessary based on the image data sent. The results of the EPMA and XRD analyses may also be managed by the host computer. It is also preferable that various training data be stored in the host computer.

[0081] The application of the nitric acid type layered double hydroxide may be performed by a robot instead of a worker, and the robot may be equipped with the above-mentioned imaging device.

[0082] In the first to third embodiments, if the reinforcing bars R, unit reinforcing bars 10, concrete structure 20, or specimen concrete 25 are to be placed in an area susceptible to salt damage, such as a coast, it is desirable to use a larger amount of nitrate-type layered double hydroxide.

[0083] Furthermore, for example, one of the multiple concrete specimens 25 may be stored in a room where the temperature and humidity are controlled within a predetermined range. The concrete specimen 25 stored in this manner is less susceptible to salt damage to the reinforcing bars R and neutralization of the concrete, and can therefore be used as a reference. Therefore, it is possible to compare the changes over time of a concrete specimen 25 placed in a location that is open to the outside air with the reference concrete specimen 25.

[0084] Furthermore, among the multiple concrete specimens 25, for example, immediately after constructing one concrete specimen 25, specific elements (e.g., Al, Ca, Cl, K, Na, O, Si) can be mapped using EPMA analysis, and this mapped element can be used as a reference to compare with subsequent mapping of the concrete specimen 25, thereby making it possible to know how the concrete specimen 25 changes over time.

[0085] REFERENCE SIGNS LIST 1 Coating agent application device 2 Conveyor device 4 Application device 6 First control device 10 Unit reinforcing bar 11 Main bar 12 Stirrup bar 13 Web bar 14 Binding wire 20 Concrete structure 25 Test specimen concrete

Claims

1. The chemical formula is M 2+ 1-x M 3+ x (OH) 2 (NO 3 - ) x / n ·mH 2 O, a layered double hydroxide, wherein M 2+ is a divalent metal, M 3+ is a trivalent metal, 0 < x < 1, m is a number greater than 0, and n is a natural number), which is provided before or after placing concrete of a concrete structure; A step of placing a first concrete specimen containing the aforementioned layered double hydroxide, having the same composition as the concrete structure but being smaller in size, near the concrete structure, A method for repairing a concrete structure, comprising the step of applying the layered double hydroxide to the concrete structure and the first test specimen concrete based on the condition of the first test specimen concrete after a predetermined time has elapsed since the construction of the concrete structure.

2. The method for repairing a concrete structure according to Claim 1, wherein the layered double hydroxide is not applied to the area exposed by cutting out the first concrete specimen.

3. A step of injecting the layered double hydroxide into the voids of the concrete structure, A method for repairing a concrete structure according to claim 1, comprising the step of injecting the layered double hydroxide into the voids of the first concrete specimen.

4. The first concrete test specimens are arranged in multiple separate locations. A method for repairing a concrete structure according to claim 1, comprising the step of estimating locations in the concrete structure that are prone to deterioration based on the condition of the multiple first concrete test specimens arranged at a distance from each other.

5. The method for repairing a concrete structure according to claim 1, wherein the portion revealed by cutting out the first concrete specimen is excluded from comparison with the concrete structure.

6. A step of providing a second concrete specimen, which does not contain the aforementioned layered double hydroxide, has the same composition as the aforementioned concrete structure, and is smaller in size, near the first concrete specimen, A method for repairing a concrete structure according to claim 1, comprising the step of comparing the deterioration of the first concrete specimen and the second concrete specimen.

7. The method for repairing a concrete structure according to claim 1, wherein the concrete structure and the first test specimen concrete are made of concrete from the same lot.

8. A method for repairing a concrete structure according to claim 1, comprising comparing the carbon dioxide content of the first concrete specimen with the carbon dioxide content of the concrete structure before the placement of the concrete structure.