Reinforcement method for existing hollow columns

Abstract

This invention provides a reinforcement method for existing hollow columns that offers sufficient reinforcement strength and can be easily implemented on-site, regardless of the location where the hollow column is erected. [Solution] A method for reinforcing existing hollow columns, in which a non-foaming polyurethane resin with a compressive strength of 15 to 100 MPa is filled into the hollow portion 1a of the existing hollow column 1 to a height of 25 to 100% from the base end 1b of the existing hollow column 1, without using aggregate.

Description

Technical Field

[0001] The present invention relates to a method for reinforcing an existing hollow column damaged by deterioration.

Background Art

[0002] Existing hollow columns such as hollow concrete utility poles may develop cracks and peeling due to aging deterioration since they were newly installed, which may lead to serious accidents such as breakage and collapse.

[0003] As a method for repairing and reinforcing utility poles to prevent such accidents, a method of winding a reinforcing plate such as an iron plate or a fiber reinforcing sheet such as polyamide around the outer periphery of the hollow column is known (for example, Patent Documents 1 and 2). In addition, a method of filling the hollow portion inside the utility pole with a foamed urethane resin has also been proposed (for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the reinforcement method by winding a reinforcing plate or a reinforcing sheet around the outer periphery of the hollow column as described in Patent Documents 1 and 2 may be difficult to construct due to obstacles in narrow locations or near the ground surface. In addition, it often takes time for the adhesive to cure, requires a large number of man-hours, and often requires skilled skills.

[0006] On the other hand, in the reinforcement method using foamed urethane resin as described in Patent Document 3, the porosity of the resin filling the hollow part inside the utility pole is high, which can easily lead to uneven density distribution of the resin and uneven reinforcement. In addition, the resin density is low, and sufficient reinforcement strength cannot be obtained.

[0007] Therefore, even when existing hollow columns are located in narrow spaces or near obstacles, there was a need for simple yet sufficiently strong reinforcement measures to prevent breakage, collapse, etc.

[0008] This invention has been made in view of the above circumstances, and aims to provide a method for reinforcing existing hollow columns that can be easily implemented on-site regardless of the location where the hollow column is erected, while providing sufficient reinforcing strength. [Means for solving the problem]

[0009] This invention is based on the discovery that hollow columns can be easily reinforced with sufficient strength without using aggregate by using non-foaming urethane resin.

[0010] The present invention provides the following means. [1] A method for reinforcing existing hollow columns, wherein the hollow portion of an existing hollow column is filled with non-foaming polyurethane resin having a compressive strength of 15 to 100 MPa, without using aggregate, up to a height of 25 to 100% from the base of the existing hollow column. [2] A method for reinforcing existing hollow columns of [1], wherein the non-foaming urethane resin is filled by injecting a urethane resin raw material liquid and allowing it to harden. [3] The method for reinforcing an existing hollow column according to [2], wherein the urethane resin raw material liquid is injected from the end or side opening of the existing hollow column. [4] A reinforcement method for an existing hollow column, which is a concrete column, as described in [1] to [3]. [5] A method for reinforcing an existing hollow pole, which is a utility pole, according to any of [1] to [4]. [6] The non-foaming urethane resin is a two-component urethane resin, and the reinforcement method for existing hollow columns is one of [1] to [5]. [Effects of the Invention]

[0011] According to the construction method of the present invention, existing hollow columns can be easily reinforced with sufficient strength on-site, regardless of the location where the hollow columns are erected. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram illustrating the construction method of the present invention. [Figure 2] This is a schematic diagram illustrating the pole bending test in the embodiment. [Modes for carrying out the invention]

[0013] The definitions and meanings of terms and notations used in this specification are given below. Non-foaming polyurethane resin means that it is not foamed polyurethane resin, and refers to polyurethane resin that is not intended to contain air bubbles through the addition of foaming agents or forced foaming. Air bubbles that are unavoidable due to the incorporation of air are not considered foaming. Numerical ranges expressed using "~" indicate that the numbers before and after "~" are the lower and upper limits. For numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in stages may be combined independently. The lower and upper limits of a numerical range may be replaced with the numbers described in the examples. The isocyanate index is the percentage of moles of isocyanate groups in polyisocyanate relative to 1 mole of hydroxyl groups in the urethane resin raw material liquid. The number of moles of hydroxyl groups in the polyol is based on the average hydroxyl value of the polyol.

[0014] The present invention provides a method for reinforcing existing hollow columns, which involves filling the hollow portion of an existing hollow column with a non-foaming urethane resin having a compressive strength of 15 to 100 MPa, without using aggregate, up to a height of 25 to 100% from the base of the existing hollow column.

[0015] Even if the existing hollow column has risks such as breakage or collapse due to aging deterioration since its installation, and it may be difficult to immediately replace it, emergency measures such as repair or reinforcement may be taken. The construction method of the present invention is useful as a method for reinforcing such an existing hollow column, and can perform reinforcement to prevent breakage or collapse with simplicity and sufficient strength. According to the construction method of the present invention in which non-foamed urethane resin is filled into the hollow column, whether the existing hollow column is in a place where large vehicles or equipment can be placed, or in a narrow area or near an obstacle, it can be carried out with relatively short construction period, simplicity and sufficient strength, and reinforcement to prevent breakage or collapse can be performed without requiring skilled skills.

[0016] In addition, in the construction method of the present invention, by using non-foamed urethane resin, it is less likely to cause uneven density distribution of the filled resin than in the case of using foamed urethane resin (polyurethane foam). Furthermore, non-foamed urethane resin is likely to be evenly filled even when there are irregularities on the inner surface forming the hollow part of the existing hollow column. For this reason, uneven reinforcement of the existing hollow column by the filled non-foamed urethane resin is less likely to occur, and breakage or collapse is more easily prevented. Also, since the resin density is high, it is easy to ensure strength to prevent breakage or collapse.

[0017] The construction method of the present invention is a method for reinforcing an existing hollow column without using aggregate. According to the construction method of the present invention, uneven density distribution of the filled resin is less likely to occur, and the existing hollow column can be reinforced with sufficient strength without the need for preparation and handling work burden of aggregate. In addition, the aggregate in the present invention refers to a solid substance (for example, powders such as silica and alumina, glass fiber, resin or metal short fiber, etc.) blended for the purpose of reinforcing the resin filled into the existing hollow column. Aggregate does not include fillers (filler materials) for cost reduction or volume increase, and solid additives not intended for reinforcement effect.

[0018] Hereinafter, a method for reinforcing an existing hollow column according to an embodiment of the present invention (hereinafter referred to as this embodiment) will be described with reference to the schematic view of the existing hollow column shown in FIG. 1. In the construction method of this embodiment, non-foamed urethane resin is filled up to a predetermined height position of the hollow part 1a of the existing hollow column 1 erected on the ground 2.

[0019] The material of the existing hollow column 1 is not particularly limited, and examples thereof include concrete columns, metal columns such as steel and aluminum, stone columns, wooden columns, and the like. The construction method of this embodiment is particularly preferably applied to an existing hollow column of a concrete column in order to prevent breakage or collapse of the hollow column.

[0020] The shape of the existing hollow column 1 is not particularly limited, and for example, it may be cylindrical or prismatic, and may also be tapered with a constant diameter or with the diameter increasing from the end opening 1c toward the base opening 1b. The size of the existing hollow column 1 is not particularly limited, and usually, it may be a size that is erected, and for example, in the case of a concrete utility pole, the length is 7 to 17 m, and the diameter is generally such that the end diameter (upper part) is 14 to 19 cm and the base diameter (bottom part) is 23 to 40 cm.

[0021] The non-foamed urethane resin is filled up to a position where the height from the base opening 1b of the existing hollow column 1 is 25 to 100%. When the non-foamed urethane resin is filled up to the position where the height from the base opening 1b of the existing hollow column 1 is 100%, that is, over the entire hollow part 1a, the existing hollow column 1 becomes a state without a hollow part and is reinforced with high strength and sturdiness. In this case, a large amount of non-foamed urethane resin is required to be filled. Usually, the existing hollow column 1 is buried in the ground 2 and erected up to a position where the height from the base opening 1b is about 15 to 25%. Therefore, in view of the balance between the construction cost and work load and the strength of the existing hollow column 1 after reinforcement, the filling of the non-foamed urethane resin may be at a position where the height from the base opening 1b of the existing hollow column 1 is 25% or more. From such a viewpoint, the height position where the non-foamed urethane resin is filled is preferably 25 to 75% from the base opening 1b of the existing hollow column 1, and more preferably 25 to 60%.

[0022] Non-foaming polyurethane resin with a compressive strength of 15 to 100 MPa is used. The compressive strength referred to here is the value measured according to the method in accordance with JIS K 6911:1995. By using non-foaming polyurethane resin with a compressive strength within the above range, the risk of fracture or collapse of the existing hollow column 1 can be suppressed, and it can be effectively reinforced without the use of aggregate. Even if the hollow section 1a of an existing hollow column 1 is filled with a predetermined amount, if the compressive strength is less than 15 MPa, the bending strength of the erected column will be insufficient. On the other hand, if the compressive strength exceeds 100 MPa, the deflection of the erected column will be insufficient, making it prone to breakage or collapse. The compressive strength of the non-foamed urethane resin is preferably 20 to 90 MPa, more preferably 25 to 80 MPa.

[0023] The non-foaming urethane resin that fills the hollow portion 1a of the existing hollow column 1 has a bending strength of preferably 25 to 120 MPa, more preferably 30 to 110 MPa, and even more preferably 35 to 100 MPa, from the viewpoint of suppressing the risk of breakage or collapse of the existing hollow column 1 and providing better reinforcement. From a similar viewpoint, the flexural modulus of non-foamed urethane resin is preferably 450 to 3000 MPa, more preferably 600 to 2800 MPa, and even more preferably 700 to 2500 MPa. From a similar viewpoint, the bending deflection of the non-foamed urethane resin is preferably 3.0 to 25.0 mm, more preferably 4.0 to 20.0 mm, and even more preferably 5.0 to 15.0 mm. The bending strength, bending modulus, and bending deflection mentioned herein are also values ​​measured according to the method conforming to JIS K 6911:1995.

[0024] The non-foaming urethane resin that fills the hollow portion 1a of the existing hollow column 1 is preferably one that has been cured by injecting urethane resin raw material liquid A. By injecting the urethane resin raw material liquid A into the hollow portion 1a of the existing hollow column 1, it is possible to easily construct the column on-site with compact equipment without the need for the burden of attaching reinforcing members around or outside the existing hollow column 1, or requiring skilled labor.

[0025] It is preferable to inject the urethane resin raw material liquid A through the end opening 1c or side opening 1d of the existing hollow column 1. It is not necessary to provide a new inlet for injecting the urethane resin raw material liquid A into the hollow portion 1a of the existing hollow column 1. The side opening 1d is, for example, a hole (opening) provided on the side of the existing hollow column 1 for purposes such as drawing in an earth wire or installing scaffolding bolts. By utilizing such an existing side opening 1d, the urethane resin raw material liquid A can be injected into the hollow portion 1a of the existing hollow column 1 from a position lower than the bottom opening 1c.

[0026] The method for injecting the urethane resin raw material liquid A is not particularly limited. For example, the urethane resin raw material liquid A, which is filled in a container such as a tank, can be pumped through a pipe to the inlet at the end port 1c or side opening 1d of the existing hollow column 1, and then injected into the hollow portion 1a of the existing hollow column 1.

[0027] In this embodiment, the construction method does not use aggregates; therefore, the urethane resin raw material liquid A does not contain aggregates and is not used in combination with aggregates. By not using aggregates, the workload of mixing the urethane resin raw material liquid A uniformly is reduced, and uneven density distribution of the filled resin is less likely to occur. Furthermore, it has the advantage that the urethane resin raw material liquid A can be easily injected even through the side opening 1d of the existing hollow column 1, and that crane equipment or the like is not required for working at higher altitudes.

[0028] For non-foaming urethane resins, a two-component urethane resin is preferred from the viewpoint of ease of handling at sites where existing hollow columns to be reinforced exist, and the ease with which various strengths such as the compressive strength mentioned above can be obtained to a sufficient degree. In other words, a type in which the urethane resin raw material liquid A is used by mixing two liquids, a first liquid of a polyol composition and a second liquid of polyisocyanate, is preferred. From the viewpoint of reducing the workload on-site and ease of handling, it is preferable to use a polyol premix in which each component is pre-mixed.

[0029] If the urethane resin raw material liquid A is a two-component mixture type, for example, it is preferable to pump the first liquid and the second liquid, each filled in a separate container, through a pipe to the injection port at the end end 1c or side opening 1d of the existing hollow column 1 at the site where the existing hollow column 1 is located, mix them with a mixing head just before injection, and then pour them into the hollow portion 1a of the existing hollow column 1.

[0030] The polyol composition used in the urethane resin raw material liquid A preferably contains a polyol and a catalyst, and is substantially free of a blowing agent. The content of the polyol composition in the urethane resin raw material liquid A is preferably 45.0 to 80.0 parts by mass, more preferably 50.0 to 75.0 parts by mass, and even more preferably 55.0 to 70.0 parts by mass, per 100 parts by mass of the urethane resin raw material liquid A, in order to obtain a non-foaming urethane resin with good strength characteristics.

[0031] As the polyol, a compound having two or more hydroxyl groups in one molecule and capable of producing polyurethane through reaction with polyisocyanate is used. Examples of polyols include polyether polyols, polyester polyols, polylactone polyols, polycarbonate polyols, and polymer polyols. The polyol may be used alone or in combination of two or more. Of these, polyether polyols are preferred because they easily yield non-foaming urethane resins with good strength properties.

[0032] Examples of polyether polyols include polymers obtained by ring-opening polymerization of alkylene oxides such as ethylene oxide and propylene oxide, or tetrahydrofuran, to an initiator having two or more active hydrogen atoms in one molecule. Examples of initiators include diols such as ethylene glycol, propylene glycol, butylene glycol, 1,6-hexanediol, and bisphenol A; triols such as glycerin and trimethylolpropane; tetraols such as pentaerythritol; and amines such as ethylenediamine and butylenediamine.

[0033] Polyols are preferable because they readily yield non-foaming urethane resins with easy-to-handle viscosity and good strength properties, and therefore have an average hydroxyl value of preferably 250-450 mgKOH / g, more preferably 255-430 mgKOH / g, and even more preferably 260-410 mgKOH / g. The hydroxyl value of polyols is determined by measurement in accordance with JIS K 1557-1:2007. When two or more polyols are used in combination, in this specification, the weighted average value based on the mass of each polyol is considered to be the average hydroxyl value of the polyols.

[0034] The catalyst in the polyol composition is preferably a urethane catalyst that promotes the reaction between the polyol and the polyisocyanate. Examples of urethane catalysts include amine catalysts; organometallic catalysts such as organobismuth compounds, organotin compounds, and acetylacetone metal salts. The catalyst may be used alone or in combination of two or more. Of these, amine catalysts are preferred from the viewpoint of ease of handling. The polyol composition may also contain a trimerizing catalyst.

[0035] Examples of amine catalysts include pentamethyldiethylenetriamine, triethylamine, N-methylmorpholine bis(2-dimethylaminoethyl) ether, bis(2-dimethylaminoethyl) ether, N,N,N',N”,N”-pentamethyldiethylenetriamine, N,N,N'-trimethylaminoethyl-ethanolamine, bis(2-dimethylaminoethyl) ether, N-methyl-N',N'-dimethylaminoethylpiperazine, N,N-dimethylcyclohexylamine, diazabicycloundecene, triethylenediamine, tetramethylethylenediamine, tetramethylhexamethylenediamine, trimethylaminoethylpiperazine, tripropylamine; and imidazole compounds such as 1-methylimidazole, 1,2-dimethylimidazole, and 1-isobutyl-2-methylimidazole. From the viewpoint of controlling the reaction rate appropriately, imidazole compounds are preferred as amine catalysts, and among them, 1-isobutyl-2-methylimidazole is more preferred.

[0036] From the viewpoint of appropriate reactivity, the catalyst content in the polyol composition is preferably 0.005 to 0.5 parts by mass, more preferably 0.01 to 0.2 parts by mass, and even more preferably 0.02 to 0.1 parts by mass, per 100 parts by mass of polyol.

[0037] In this embodiment, the polyol composition preferably contains an antifoaming agent to suppress foaming and facilitate the acquisition of a non-foaming urethane resin. Generally, compounds with an HLB value of about 1 to 3, which represents the hydrophilic-lipophilic balance, are used as antifoaming agents. Examples of antifoaming agents include silicone-based antifoaming agents (oil type, compound type, self-emulsifying type, emulsion type, etc.), fatty acid esters, metal soaps, phosphate esters, nonionic surfactants, etc. The antifoaming agent may be used alone or in combination of two or more. Of these, silicone-based antifoaming agents are preferred from the viewpoint of good foam suppression.

[0038] The amount of defoaming agent in the polyol composition is preferably 0.1 to 2.0 parts by mass, more preferably 0.2 to 1.0 parts by mass, and even more preferably 0.3 to 0.7 parts by mass, per 100 parts by mass of polyol, from the viewpoint of suppressing foaming of the non-foaming urethane resin and providing good strength characteristics.

[0039] In this embodiment, the polyol composition is preferably substantially free of foaming agents in order to obtain a non-foaming urethane resin with good strength properties. Although water can act as a foaming agent, "substantially" here means that water that may be included inevitably or as a medium in the compounding components is not considered a foaming agent. Therefore, from the viewpoint of suppressing the action of water contained in the polyol composition as a foaming agent, it is preferable to incorporate a dehydrating agent into the polyol composition.

[0040] Examples of dehydrating agents include zeolite, silica gel, calcium oxide, activated carbon, potassium hydroxide, sodium hydroxide, and lithium hydroxide. The dehydrating agent may be used alone or in combination of two or more. Of these, zeolite is preferred from the viewpoint of ease of handling.

[0041] If the polyol composition contains a dehydrating agent, its content is preferably 0.1 to 10.0 parts by mass, more preferably 1.0 to 10.0 parts by mass, and even more preferably 5.0 to 10.0 parts by mass, per 100 parts by mass of polyol, from the viewpoint of suppressing foaming of the non-foamed urethane resin and providing good strength characteristics.

[0042] In this embodiment, the polyol composition preferably contains a flame retardant from the viewpoint of imparting flame retardancy to the non-foaming urethane resin. As the flame retardant, a liquid flame retardant that is liquid at room temperature (20°C) is preferred from the viewpoint of making the polyol composition easy to handle. The flame retardant may also contain a powdered flame retardant.

[0043] Examples of flame retardants include monophosphate esters and condensed phosphate esters. The flame retardant may be used alone or in combination of two or more types. Of these, monophosphate esters are preferred. Examples of monophosphate esters include trialkyl phosphates such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, and tri(2-ethylhexyl) phosphate; halogen-containing phosphate esters such as tris(β-chloropropyl) phosphate; trialkoxy phosphates such as tributoxyethyl phosphate; and aromatic ring-containing phosphate esters such as tricresyl phosphate, trixylenyl phosphate, tris(isopropylphenyl) phosphate, cresyldiphenyl phosphate, and diphenyl(2-ethylhexyl) phosphate. Among these, halogen-containing phosphate esters such as tris(β-chloropropyl) phosphate are preferred.

[0044] If the polyol composition contains a flame retardant, the amount is preferably 5.0 to 50.0 parts by mass, more preferably 5.0 to 30.0 parts by mass, and even more preferably 10.0 to 20.0 parts by mass, per 100 parts by mass of polyol, from the viewpoint of flame retardancy and good strength characteristics of the non-foamed urethane resin.

[0045] In this embodiment, the polyol composition preferably contains a viscosity reducer to make it easier to handle and to facilitate mixing with polyisocyanate. A polyether compound is preferred as the viscosity reducer, having a structure in which one or both hydroxyl groups at one or both ends of a polyoxyalkylene glycol are replaced with alkoxy groups or alkylene oxy groups having 3 or more carbon atoms. When both hydroxyl groups are replaced, the replaced alkoxy groups or alkylene oxy groups may be the same or different. Examples of viscosity reducers include polyoxypropylene monobutyl ether, triethylene glycol monobutyl ether, polyoxyethylene polyoxypropylene monobutyl ether, and polyoxyethylene monobutyl ether. The viscosity reducer may be used alone or in combination of two or more. Of these, triethylene glycol monobutyl ether is preferred.

[0046] If the polyol composition contains a viscosity reducer, its content is preferably 1.0 to 25.0 parts by mass, more preferably 5.0 to 25.0 parts by mass, and even more preferably 10.0 to 20.0 parts by mass, per 100 parts by mass of the polyol composition, from the viewpoint of ease of handling of the polyol composition and ease of mixing with polyisocyanate.

[0047] The polyol composition in this embodiment may contain other additives as needed, provided that it does not impair the good miscibility with polyisocyanate and the good strength properties of the non-foaming urethane resin. Examples of other additives include antioxidants (phenol-based, amine-based, sulfur-based, etc.), heat stabilizers, antistatic agents, stabilizers, crosslinking agents, lubricants, softeners, and pigments. These additives may be used individually or in combination of two or more.

[0048] The polyisocyanate to be mixed and reacted with the polyol composition is an isocyanate having two or more isocyanate groups in one molecule, and various aromatic, alicyclic, and aliphatic polyisocyanates can be used. One type of polyisocyanate may be used alone, or two or more types may be used in combination. Of these, aromatic polyisocyanates are preferred because they easily produce non-foaming urethane resins with good strength properties, and furthermore, aromatic polyisocyanates that are liquid at room temperature (20°C) are preferred from the viewpoint of ease of handling.

[0049] Examples of aromatic polyisocyanates include phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate (MDI), dimethyldiphenylmethane diisocyanate, triphenylmethane triisocyanate, naphthalene diisocyanate, and polymethylene polyphenyl polyisocyanate (polymeric MDI). Among these, polyisocyanate MDI and polymeric MDI are preferred from the viewpoint of ease of handling and appropriate reactivity, and because they make it easy to obtain non-foaming urethane resins with good strength properties. Polycyanates obtained by modifying MDI with carbodiimide are also preferred.

[0050] The isocyanate index when reacting a polyol composition with a polyisocyanate to obtain a non-foaming urethane resin is not particularly limited and is usually around 100, but from the viewpoint of obtaining a non-foaming urethane resin with good strength properties, it is preferably 80 to 120, more preferably 82 to 115, and even more preferably 84 to 110.

[0051] In order to obtain a non-foaming urethane resin with good strength characteristics, the total amount of the polyol composition and polyisocyanate in the urethane resin raw material liquid A is preferably 90.0 to 100 parts by mass, more preferably 95.0 to 100 parts by mass, and even more preferably 100 parts by mass, per 100 parts by mass of the urethane resin raw material liquid A. When the total amount of the polyol composition and polyisocyanate is less than 100 parts by mass, other substances that can be added to the urethane resin raw material liquid A besides the polyol composition and polyisocyanate include, for example, the same substances as the other additives in the polyol composition described above.

[0052] The work process in the construction method of this embodiment only requires injecting the urethane resin raw material liquid A into the hollow portion 1a of the existing hollow column 1. The urethane resin raw material liquid A injected into the hollow portion 1a of the existing hollow column 1 can be left to harden, and for example, it will reach a strength of about 80% of its final strength in 24 hours, which has the advantage of a short construction period. In order to obtain a non-foaming urethane resin with good strength characteristics, the urethane resin raw material liquid A can be sufficiently hardened by leaving it for at least 3 days, more preferably 4 days or more, and even more preferably 5 days or more. [Examples]

[0053] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples, and various modifications are possible without departing from the spirit of the invention.

[0054] [Urethane resin used] As non-foaming polyurethane resins, polyurethane resins P1 to P4 shown in Table 1 were used. The details of the raw material components of polyurethane resins P1 to P4 shown in Table 1 are as follows. • KC-209: "Sannix (registered trademark) KC-209", manufactured by Sanyo Chemical Industries, Ltd., polyether polyol (initiator: glycerin), hydroxyl value 34 mg KOH / g • FA-908: "Sannix (registered trademark) FA-908", manufactured by Sanyo Chemical Industries, Ltd., polyether polyol (initiator: glycerin), hydroxyl value 24 mg KOH / g ·EL-410NE: "Exsenol (registered trademark) 410NE", manufactured by AGC Inc., polyether polyol (initiator: pentaerythritol), hydroxyl value 400 mg KOH / g • SP-750: "Sannix (registered trademark) SP-750", manufactured by Sanyo Chemical Industries, Ltd., polyether polyol (initiator: sorbitol), hydroxyl value 490 mg KOH / g • NP-300: "Sannix (registered trademark) NP-300", manufactured by Sanyo Chemical Industries, Ltd., polyether polyol (initiator: ethylenediamine), hydroxyl value 755 mg KOH / g • 14BG: 1,4-butanediol, manufactured by Mitsubishi Chemical Corporation • KL-120: "Kaorizer (registered trademark) No. 120", manufactured by Kao Corporation, 1-isobutyl-2-methylimidazole • BYK-A506: Silicone-based defoaming agent manufactured by BYK Corporation. • TMCPP: Tris(chloropropyl) phosphate, manufactured by Daihachi Chemical Industry Co., Ltd. • BTG: "Butyl triglycol", Nippon Emulsifier Co., Ltd., Triethylene glycol monobutyl ether • Molecular sieve 3A: Manufactured by Resonaq Universal Co., Ltd., zeolite • MR-200: "Millionate (registered trademark) MR-200", manufactured by Tosoh Corporation, polymethylene polyphenyl polyisocyanate (polymeric MDI) • MTL: "Millionate (registered trademark)", manufactured by Tosoh Corporation, carbodiimide-modified phenylmethane diisocyanate (monomeric MDI)

[0055] Polyol compositions formulated according to the compositions shown in Table 1 were mixed with polyisocyanate by stirring, and the resulting urethane resin raw material liquid was poured into a mold and allowed to stand for 2 hours. The cured urethane resin was demolded, and non-foaming urethane resin test specimens for strength measurement were prepared. The molded size of the test specimen for compressive strength measurement (compression test) was 150 mm x 150 mm with a thickness of 12.7 mm, while the molded size of the test specimen for flexural strength, flexural modulus, and flexural deflection (flexural test) was 150 mm x 150 mm with a thickness of 4 mm.

[0056] The compressive strength, flexural strength, flexural modulus, and flexural deflection of the urethane resins shown in Table 1 were measured according to the method conforming to JIS K 6911:1995.

[0057] [Table 1]

[0058] [Column bending test] We assessed the feasibility of preventing collapse of a simulated deteriorated reinforced concrete column, assuming that the tensile steel members of the column had fractured due to lateral cracking. Figure 2 shows an overview of the column bending test. The deteriorated simulated column was fabricated by creating a half-section cut section 11f by chipping away at the concrete portion from the outer surface with a grinder at a position 600 mm below the ground-level marker line 11e (2.5 m from the base opening 11b) of a reinforced concrete column with a length of 12 m or 15 m, and cutting the exposed reinforcing bars. After erecting a deteriorated simulated column in ground 12 equivalent to soil type B, a urethane resin raw material liquid was injected into the hollow part of the column from the top end 11c, and left for 5 days to produce a hollow column test specimen 11 in which non-foaming urethane resin was filled to a predetermined height (height from the base end 11b). A column bending test was conducted on a hollow column test specimen 11 by applying a horizontal load P in the opposite direction to the surface (half-section cut section 11f) where a half-section cut was made, at a position 250 mm from the tip 11c. The horizontal load P was applied by pulling a wire 14 connected through a pulley 15 attached to the reaction column 13 using a winch. The test results are shown in Table 2.

[0059] The load at which the hollow column test specimen 11 collapsed or broke was defined as the maximum load, and the safety factor was calculated. The safety factor is the ratio of the maximum load to the design load (maximum load / design load). The design load for the reinforced concrete column of the hollow column test specimen 11 is defined as 3.43kN for a 12m column and 4.91kN for a 15m column. A safety factor of 1.0 or higher indicates sufficient resistance to horizontal loads.

[0060] Furthermore, we determined whether the hollow column test specimen would collapse when its tip position was displaced by 2.5m. In Table 2, cases where it did not collapse are indicated as A, and cases where it collapsed are indicated as B. In Table 2, the filling height is the height from the base opening 11b of the non-foamed urethane resin filling in the hollow column test specimen 11. Comparative Example 1 is an unfilled hollow column test specimen (blank).

[0061] [Table 2]

[0062] As can be seen from the column bending test results shown in Table 2, when a deteriorated simulated column is filled with non-foaming urethane resin with a compressive strength within a specified range to a height of 25% or more (Examples 1-5), a sufficient safety factor is achieved, and it was confirmed that collapse can be prevented even when a horizontal load causing a 2.5m displacement at the top is applied. [Explanation of Symbols]

[0063] 1 Existing hollow column 1a Hollow part 1b, 11b Motoguchi 1c, 11c end 1d side opening A. Urethane resin raw material liquid 2, 12 Ground 11 Hollow column test specimen 11e Ground marking line 11f Half-section cutting section 13 Reaction Column 14 wires 15 Pulleys

Claims

1. A method for reinforcing existing hollow columns, in which a non-foaming polyurethane resin with a compressive strength of 15 to 100 MPa is filled into the hollow portion of the existing hollow column, without using aggregate, up to a height of 25 to 100% from the base of the existing hollow column.

2. A method for reinforcing an existing hollow column according to claim 1, wherein the non-foaming urethane resin is filled by injecting a urethane resin raw material liquid and allowing it to harden.

3. The method for reinforcing an existing hollow column according to claim 2, wherein the urethane resin raw material liquid is injected from the end or side opening of the existing hollow column.

4. The method for reinforcing an existing hollow column according to claim 1 or 2, wherein the existing hollow column is a concrete column.

5. The method for reinforcing an existing hollow pole according to claim 1 or 2, wherein the existing hollow pole is a utility pole.

6. The method for reinforcing an existing hollow column according to claim 1 or 2, wherein the non-foaming urethane resin is a two-component urethane resin.

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