Method of formation of compression-bonded structure

In a bonding structure for bonding a bonding attachment, having an insertion hole formed to allow insertion of a rebar therein, to the rebar, an application liquid mixed with a granular fine powder is previously applied on the rebar or the inside of the insertion hole of the bonding attachment, and then the bonding attachment is bonded to the rebar inserted in the insertion hole. Thereby, the granular fine powder is disposed on the contact surfaces of the bonding attachment and the rebar inserted in the insertion hole of the bonding attachment, increasing the friction force to resist against the force to pull the inserted rebar out from the insertion hole.

This application is a national phase entry under 35 U.S.C. § 371 of PCT Patent Application No. PCT/JP2012/083334, filed on Dec. 21, 2012, which claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2011-280191, filed Dec. 21, 2011, and Japanese Patent Application No. 2012-194186, filed Sep. 4, 2012, all of which are incorporated by reference.

TECHNICAL FIELD

The present invention relates to a bonding structure of a rebar and a bonding attachment and a method of bonding a rebar and a bonding attachment, particularly, to an art to enhance the bonding strength of the rebar and the bonding attachment by bonding the rebar and the bonding attachment with a granular fine powder disposed on contact surfaces of the rebar and the bonding attachment.

BACKGROUND ART

Conventionally, a mechanical joint for connecting a pair of rebars by inserting one of end portions of a rebar and one of end portions of another rebar in a sleeve is provided.

For example, a mechanical joint is provided in Patent Literature 1, in which one of end portions of a rebar and one of end portions of another rebar are inserted in a sleeve so as to abut against each other, and then the sleeve is pressed from the outer peripheral surface to bond the sleeve to the rebar.

In such mechanical joint, predetermined tensile strength has to be secured to hold the tensile force acting on the rebar. Such tensile strength is secured by a structure having a knot provided on the peripheral surface of the rebar or a structure providing interlocking of the knot with the inner peripheral surface of the sleeve.

As for the issue of securing the pull-out strength of the rebar, Patent Literature 2 proposes a rebar providing improved bonding strength to concrete. Epoxy powder coating is sprayed on a heated rebar to form a first anticorrosion film, and on the surface of the molten first anticorrosion film, a second anticorrosion film is formed with a powder coating which is a mixture of epoxy resin and curing agent. Innumerable number of protrusion formed by the second anticorrosion film enhances the bonding strength to concrete.

Patent Literature 3 proposes a method of attaching a metal sleeve to a concrete-reinforcing bar. In the method, a particle having higher hardness than both the concrete-reinforcing bar and the sleeve is disposed between the opposing surfaces of the sleeve and the bar. By the particle interlocking with the bar and the sleeve, the sleeve is bonded to the bar with sufficient force to hold the bar and the sleeve together.

CITATION LIST

Patent Literatures

Patent Literature 1: JP 10-131303 A

Patent Literature 2: JP 2005-66574 A

Patent Literature 3: JP 53-4318 A

SUMMARY OF INVENTION

Technical Problem

Structures provided in Patent Literatures 1 and 2 enhance the tensile strength of connected bars and the pull-out strength of the rebar bonded to concrete. However, these structures are not focused on contact surfaces of the bar and the metal attachment bonded to the bar, so that these structures are not aimed to enhance the friction force between the bar and the metal attachment to secure the bonding strength of the bar and the metal attachment.

Specifically, in the method described in Patent Literature 3, a particle including a chilled steel ball or the like having a dimension of 0.8 to 1.5 mm, or a mesh size of around 16 meshes, is disposed between the sleeve and the bar, and the particle is adhered to the sleeve and the bar with an adhesive including a curing agent, such as a plastic adhesive based on epoxy resin and curing agent or a neoprene based adhesive.

In this method, the particle with such grain size and the adhesive are used to interlock the particle with the sleeve and the bar so as to enhance the bonding strength of the sleeve and the bar. However, since the viscosity of such adhesive is high, the particle is likely to sink in the adhesive, and the adhesive will harden before inserting the bar in the sleeve, making the insertion difficult. If the particle sinks in the adhesive, the particle cannot contribute to improvement of bonding strength of the sleeve and the bar. Moreover, the hardened adhesive itself reduces the friction between the sleeve and the bar, resulting in reduction of the bonding strength.

With regard to the method of forming a bonding structure of a rebar and a bonding attachment bonded to the rebar, the object of the present invention is to enhance the bonding strength of the rebar and the bonding attachment by increasing the friction force on the contact surfaces of the rebar and the bonding attachment.

Solution to Problem

According to an aspect of the present invention, to achieve the object mentioned above, a method of forming a bonding structure in which a bonding attachment having an insertion hole for inserting the rebar is bonded to a rebar includes a step of spraying an application liquid including a water-soluble resin emulsion mixed with a granular fine powder with a grain size of 180 to 600 μm on the outer peripheral surface of the rebar and/or the inner peripheral surface of an insertion hole of the bonding attachment, a step of inserting the rebar in the insertion hole of the bonding attachment, and a step of bonding the bonding attachment to the rebar by pressing the bonding attachment in which the rebar is inserted in the insertion hole.

The bonding attachment is a metal attachment to be bonded to the rebar such as a sleeve which functions as a mechanical joint connecting rebars and a metal attachment attached to the rebar to enhance the fixing force on concrete.

The grain size of the granular fine powder may be from 180 to 300 μm.

The granular fine powder may be silicon carbide based material or aluminum based material.

Advantageous Effects of Invention

According to the present invention, a granular fine powder is applied to contact surfaces of a rebar and a bonding attachment when the bonding structure of the rebar and the bonding attachment is to be formed. The bonding structure thus formed can enhance the bonding strength of the rebar and the bonding attachment by the granular fine powder disposed on the contact surfaces of the rebar and the bonding attachment increasing the friction force between the rebar and the bonding attachment.

DESCRIPTION OF EMBODIMENTS

The method of forming a bonding structure of a rebar and a bonding attachment according to the present invention will be described referring to the drawings.

The bonding structure formed by the embodiment is configured as a mechanical joint including a rebar and a sleeve which is a bonding attachment bonded to the rebar.

As illustrated inFIG. 1, in the bonding structure formed by the method of forming a bonding structure of a rebar and a bonding attachment according to the embodiment, a rebar2is inserted in each of both ends of an insertion hole1aformed in a sleeve1. The sleeve1is bonded to the rebar2to connect a pair of rebars.

The sleeve1has an approximately cylindrical shape with the insertion hole1aformed to have openings on both ends. The diameter of the insertion hole1ais slightly larger than the diameter of the rebar2so that the rebar2can be inserted in the insertion hole1a.

Further, as illustrated inFIG. 2, on contact surfaces of the inner peripheral surface of the insertion hole1aand the outer peripheral surface of the rebar2, which make contact with each other, a granular fine powder10is disposed to increase the friction force on the contact surfaces. In the embodiment, the granular fine powder10is adhered to the inner peripheral surface of the insertion hole1aand the outer peripheral surface of the rebar2with application liquid.

The granular fine powder10is an inorganic granule based fine powder such as a silicon carbide based fine powder or an aluminum based fine powder with a grain size from 180 to 600 μm. The granular fine powder10may includes a fine powder with a certain grain size from 180 to 600 μm, for example, a grain size of 300 μm, or a mixture of fine powders with grain sizes ranging from 180 to 600 μm, for example, from 200 to 400 μm.

The type of the rebar2connected in the embodiment is not particularly limited; however, the embodiment illustrates, in the drawings, a deformed bar in which knots are formed on the outer peripheral surface, parallel to each other, with a constant pitch.

Now, the method of bonding the sleeve1to the rebar2is described referring toFIGS. 3 and 4.

As illustrated inFIG. 3, an application liquid which is a mixture of a predetermined liquid and the granular fine powder10is previously applied to the inner peripheral surface of the insertion hole1aor the outer peripheral surface of the rebar2, and the rebar2is inserted in the insertion hole1aof the sleeve1from each of both ends of the insertion hole1a. The application liquid which is a mixture of the predetermined liquid and the granular fine powder10may be applied to both of the inner peripheral surface of the insertion hole1aand the outer peripheral surface of the rebar2.

The liquid for mixing the granular fine powder10therein has a predetermined viscosity providing adhesion to the surface when applied. Specifically, the liquid is a synthetic resin emulsion of a water-soluble resin using water as a dispersion medium. As a water-soluble resin, a natural water-soluble resin such as Arabian gum and dextrin, a semi-synthetic water-soluble resin such as carboxyl methylcellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, and a synthetic water-soluble resin such as polyvinyl alcohol and acrylic resin can be used.

As illustrated inFIG. 4, under the state in which the granular fine powder10is adhered to the inner peripheral surface of the insertion hole1aor the outer peripheral surface of the rebar2with the application liquid, the rebar2is inserted in the insertion hole1aand then the sleeve1is pressed radially inward from the outer peripheral surface of the sleeve1. By the pressing, the insertion hole1ashrinks to reduce the diameter and the inner peripheral surface of the insertion hole1aand the rebar2are bonded with the granular fine powder10disposed in between.

When bonding is completed, the application liquid evaporates with the help of the heat produced during bonding but the granular fine powder10remains, and thereby only the granular fine powder10is disposed between the inner peripheral surface of the insertion hole1aand the rebar2.

By the process described above, the rebar and the sleeve1are bonded with the granular fine powder10disposed between the contact surfaces. As a result, the granular fine powder10increases the friction force between the rebar2and the sleeve1, thereby enhancing the bonding strength of the rebar2and the sleeve1. Particularly, since the high friction force can be provided to the smooth surface without ribs formed on the rebar2, shorter sleeves can provide the same degree of strength as longer sleeves. The embodiment is particularly advantageous in the application where shorter sleeves are preferable.

Further, plastic working of the sleeve1performed to reduce the inner diameter of the insertion hole1aprovides high strength.

The performance is evaluated for the bonding structure formed as described above, with different grain sizes of the granular fine powder10. Test results are listed in Table 1 andFIGS. 5 to 7.

Note that, the stiffness and the slip distance are not measured for the test piece without the granular fine powder10, since the pull-out occurred in the test piece under the stress of, or below, 172.5 N/mm2which is 50% of the standard yield strength.

According to the test result, test piece D shows the highest strength, test piece B shows the second highest strength, and test piece A shows the third highest strength. Further, test piece C shows the highest stiffness, test piece B shows the second highest stiffness, test piece A shows the third highest stiffness, and test piece D shows the fourth highest stiffness. Test pieces F to H of which grain size is 75 μm or smaller show significantly lower strength than test pieces A to E.

From the test result, it is discovered that the granular fine powder10with a grain size within the range from 180 to 1180 μm is preferably used.

However, in the process before bonding the sleeve1and the rebar2, when the granular fine powder10with relatively large grain size within the range mentioned above is used, it is difficult to adhere the granular fine powder10to the outer peripheral surface of the rebar2or the inner peripheral surface of the sleeve1with the application liquid, and the adhered granular fine powder10may easily come off. Regarding this problem, by using an application liquid having higher viscosity or stronger adhesion, the granular fine powder10can be kept adhered in place without coming off. However, when such application liquid is used, the rebar2sticks to the insertion hole1aof the sleeve1upon inserting the rebar2in the sleeve1, making the insertion difficult, and also the granular fine powder10sinks in the application liquid and does not contribute to the increase in the friction force between the rebar2and the sleeve1.

Therefore, it has been studied that, to keep the granular fine powder10adhered to the rebar2or the sleeve1using the application liquid with moderate viscosity and adhesion as well as to provide sufficient strength to the bonding structure, the grain size of the granular fine powder10is preferably within the range from 180 to 600 μm, more preferably, from 180 to 300 μm.

Now, the method of forming a bonding structure of a rebar and a bonding attachment according to another embodiment of the present invention will be described.

As illustrated inFIG. 8, the bonding structure formed by the embodiment is configured as a mechanical joint. The end portion of the rebar2is inserted in one end of each of a pair of sleeves3. The other end of each of the pair of sleeves3is connected by a connector4and the granular fine powder is disposed between the sleeve3and the rebar2to bond the sleeve3and the rebar2to constitute the bonding structure.

Similarly to the sleeve1, the sleeve3has an approximately cylindrical shape with the insertion hole3aformed to have openings on both ends.

The sleeve3differs from the sleeve1in that one end of the sleeve3constitutes an insertion part31for inserting the rebar2therein, and the other end constitutes a threaded portion32for attaching the connector4thereto.

The diameter of the insertion hole3aof the insertion part31is slightly larger than the diameter of the rebar2to allow insertion of the rebar2.

On contact surfaces of the inner peripheral surface of the insertion hole3aof the insertion part31and the outer peripheral surface of the rebar2, which make contact with each other, the granular fine powder is disposed to increase the friction force on the contact surfaces. In the embodiment, the granular fine powder is adhered to the inner peripheral surface of the insertion hole3aof the insertion part31and the outer peripheral surface of the rebar2.

As described above, the granular fine powder is an inorganic granule based fine powder such as silicon carbide based fine powder or an aluminum based fine powder with a grain size from 180 to 600 μm.

The diameter of the threaded portion32is previously reduced from the diameter of the insertion part31by plastic working, so as to be slightly smaller than the diameter of the insertion part31.

An internal thread is formed in the threaded portion32so as to engage with the external thread formed on the outer peripheral surface of a connecting bolt4.

The connecting bolt4is a column-shaped member with an external thread formed on the outer peripheral surface.

The diameter of the connecting bolt4corresponds to the diameter of the insertion hole3aof the threaded portion32of the sleeve3so that the connecting bolt4can be screwed into the insertion hole3aof the threaded portion32of the sleeve3.

The axial length of the connecting bolt4is twice the length of the threaded portion32thereby allowing one end of the connecting bolt4to be screwed into the threaded portion32of one of the sleeves3as well as the other end of the connecting bolt4to be screwed into the threaded portion32of the other sleeve3. In this manner, two sleeves3, each of which with the rebar2inserted therein, can be connected together.

Now, a method of forming a bonding structure to bond the rebar2and the sleeve3will be described referring toFIG. 9.

First, two sleeves3are prepared and the rebar2is inserted in the insertion hole3aof the insertion part31of each of the sleeves3. In this process, an application liquid mixed with a granular fine powder is previously applied to the inner peripheral surface of the insertion hole3aof the sleeve3and the outer peripheral surface of the rebar2to adhere the granular fine powder on the inner peripheral surface of the insertion hole3aof the sleeve3and the outer peripheral surface of the rebar2.

Then, two sleeves3, each of which having the rebar2inserted in the insertion hole3aof the insertion part31, are placed such that the openings at the end of the threaded portions32face each other, and one or the other end of the connecting bolt4is screwed into each of the threaded portions32.

Further, the outer peripheral surface of the insertion part31having the rebar2inserted therein is pressed radially inward to carry out plastic working on the insertion part31. By the pressing, the insertion part31shrinks to reduce the diameter and the inner peripheral surface of the insertion part31and the rebar2are bonded with the granular fine powder disposed in between.

In this manner, the rebar2is bonded to the inner peripheral surface of the insertion hole3aof the insertion part31of each of two sleeves3, and the sleeves3are connected by the connecting bolt4, thereby connecting the two rebars2.

As described above, similarly to the previous embodiment, the rebar2is bonded to the sleeve3with the granular fine powder disposed on the contact surfaces of the rebar2and the sleeve3in the embodiment. As a result, the granular fine powder increases the friction force between the rebar2and the sleeve3to enhance the bonding strength of the rebar2and the sleeve3.

Note that, in the embodiment described above, the shape and the configuration of the mechanical joint are not particularly limited to those of the embodiment. Any shape and configuration allowing the rebar2to be inserted in the insertion holes1aand3aformed in the sleeves1and3, can be applied.

Further, the granular fine powder can be disposed on the contact surfaces of the rebar2and the sleeves1and3by adhering the granular fine powder on one surface of a thin sheet of which other surface is adhered to the inner peripheral surface of the insertion holes1aand3a, or by melt adhesion in which the granular fine powder is sprayed on the inner peripheral surface of the insertion holes1aand3aof the heated sleeves1and3.

In the method of forming a bonding structure of a rebar and a bonding attachment according to the embodiment, description is made for the case in which the mechanical joint for connecting rebars is formed. However, it is not limited to the embodiment. Another embodiment of the present invention may be configured as a method of forming a bonding structure of a rebar and a bonding attachment for fastening the rebar to concrete. An example of such embodiment is illustrated inFIGS. 10(A) to 10(E).

As illustrated inFIGS. 10(A) and 10(B), one end of a rebar2is inserted in an insertion hole5a, having a circular cross section, formed in a bonding attachment5having an approximately elliptical cross section. The bonding attachment5is bonded to the rebar2with a granular fine powder disposed on the inner peripheral surface of the insertion hole5aon which the bonding attachment5and the rebar2make contact.

A method of forming the bonding structure will be described referring toFIGS. 10(C) to 10(E).

First, the end portion of the rebar2is inserted in the insertion hole5a, having a circular cross section, formed in the bonding attachment5having an approximately square cross section. Then, the bonding attachment5is pressed from the outer peripheral surface by a dice51having an arc shaped groove51a. In this manner, the bonding attachment5is compressed and deforms to have a periphery having an approximately elliptic cross section, and in the same process, the bonding attachment5is bonded to the rebar2.

In the embodiment, the bonding attachment5and the rebar2are also bonded with the granular fine powder disposed on the contact surfaces of the bonding attachment5and the rebar2by applying the application liquid mixed with the granular fine powder, before bonding, on the inner peripheral surface of the insertion hole5aon which the bonding attachment5and the rebar2make contact.

Another bonding structure formed by the method of forming a bonding structure according to the embodiment is illustrated inFIGS. 11(A) to 11(E).

As illustrated inFIGS. 11(A) and 11(B), a bonding attachment6including an insertion hole6ahaving a circular cross section includes a portion with an outer periphery having a hexagonal cross section and a portion with an outer periphery having a circular cross section produced by compressing and deforming the hexagonal cross section. One of both end portions of the rebar2is inserted in the insertion hole6ain the portion having a circular cross section produced by compressing and deforming. In the portion of the insertion hole6awhere the rebar2is inserted, the bonding attachment6and the rebar2is bonded with the granular fine powder disposed in between.

A method of forming the bonding structure will be described referring toFIGS. 11(C) to 11(E).

First, the end portion of the rebar2is inserted in the insertion hole6ato half the length of the insertion hole6ahaving a circular cross section formed in the bonding attachment6having a hexagonal cross section. Then, the portion of the bonding attachment6in which the rebar2is inserted is pressed from the outer peripheral surface by a dice61having an arc shaped groove61a. In this manner, the pressed portion of the bonding attachment6is compressed and deforms to have an approximately circular cross section, and the bonding attachment6is bonded to the rebar2in the deformed portion. A step is formed on the outer periphery surface by the process of producing the bonding. Thereby, the bonding attachment6is now configured with the portion having an original hexagonal cross section and the compressed portion having a circular cross section.

In the embodiment, the bonding attachment6and the rebar2are also bonded with the granular fine powder disposed on the portion contacting each other by applying the application liquid mixed with the granular fine powder, before bonding, on the bonding attachment6or the rebar2. Further, the bonding attachment6can enhance the fixing force on concrete by the step on the outer periphery surface formed in the process of producing the bonding.

Another bonding structure formed by the method of forming a bonding structure according to the embodiment is illustrated inFIGS. 12(A) to 12(G).

As illustrated inFIGS. 12(A) and 12(B), a bonding attachment7including an insertion hole7ahaving a circular cross section includes a thin sleeve-shaped portion having a circular cross section and a thick portion of which diameter gradually increases from the end of the sleeve-shaped portion. One of ends of the rebar2is inserted in the insertion hole7aof the sleeve-shaped portion. In the portion of the insertion hole7awhere the rebar2is inserted, the bonding attachment7is bonded to the rebar2with the granular fine powder disposed in between.

A method of forming the bonding structure will be described referring toFIGS. 12(C) to 12(G).

First, chucks73and74are attached to the sleeve-shaped bonding attachment7with an insertion hole7ahaving a circular cross section formed therein. Then, a dice72having a column-shaped protrusion which can be inserted in the inner circumference of the thin portion is pressed on to the end portion of the thin portion. Thus, the end portion of the thin portion is stretched to increase the diameter, and then pressed by the flat portion of the dice72to expand. Thereby, the thin portion expands toward the end. Then, the rebar2is inserted in the insertion hole7ain the thick portion which is not expanded. The portion of the bonding attachment7in which the rebar2is inserted is pressed from the outer peripheral surface by a dice71having an arc shaped groove71a. In this manner, the pressed portion of the bonding attachment7is compressed and deforms, and the bonding attachment7is bonded to the rebar2.

In the embodiment, the bonding attachment7and the rebar2are also bonded with the granular fine powder disposed on the portion contacting each other by applying the application liquid mixed with the granular fine powder, before bonding, on the bonding attachment7or the rebar2. Further, the bonding attachment7can enhance the fixing force on concrete by the portion expanding toward the end.

Another bonding structure formed by the method of forming a bonding structure according to the embodiment is illustrated inFIGS. 13(A) to 13(G).

As illustrated inFIGS. 13(A) and 13(B), a bonding attachment8including an insertion hole8ahaving a circular cross section includes a sleeve-shaped portion having a circular cross section and a portion which expands from the end portion of the sleeve-shaped portion and then is folded inward. One of ends of the rebar2is inserted in the insertion hole8aof the sleeve-shaped portion. At the portion of the insertion hole8ain which the rebar2is inserted, the bonding attachment8is bonded to the rebar2with the granular fine powder disposed in between.

A method of forming the bonding structure will be described referring toFIGS. 13(C) to 13(G).

First, chucks83and84are attached to the sleeve-shaped bonding attachment8with an insertion hole8ahaving a circular cross section formed therein. The dice82is subsequently pressed on to the end surface of the bonding attachment8. Thereby, the end surface buckles to expand outward. By further pressing the dice82, the end surface is folded in a two-fold shape. The rebar2is inserted in the insertion hole88in the sleeve-shaped portion. The portion of the bonding attachment8in which the rebar2is inserted is pressed from the outer peripheral surface by a dice81having an arc shaped groove81a. In this manner, the pressed portion of the bonding attachment8is compressed and deforms, and the bonding attachment8is bonded to the rebar2.

In the embodiment, the bonding attachment8and the rebar2are also bonded with the granular fine powder disposed on the portion contacting each other by applying the application liquid mixed with the granular fine powder, before bonding, on the bonding attachment8or the rebar2. Further, the bonding attachment8can enhance the fixing force on concrete by the portion expanding toward the end.

Further, a bonding structure according to another embodiment formed by the method of forming a bonding structure according to the embodiment is illustrated inFIGS. 14(A) to 14(F).

As illustrated inFIGS. 14(A) and 14(B), a bonding attachment9including an insertion hole9aincluding a sleeve-shaped portion in which the insertion hole9ahaving an approximately rectangular cross section with round corners is formed and a portion, in which the insertion hole9ahaving a circular cross section is formed, expanding toward the end from the end portion of the sleeve-shaped portion. One end of the rebar2is inserted in the sleeve-shaped portion. At the portion of the sleeve-shaped portion in which the rebar2is inserted, the bonding attachment9is bonded to the rebar2with the granular fine powder disposed in between.

A method of forming the bonding structure will be described referring toFIGS. 14(C) to 14(G).

First, the periphery of the sleeve-shaped portion is pressed from four directions by four trapezoidal dices91to form the insertion hole9ahaving an approximately rectangular cross section with round corners. Then, the located end portion of the rebar2is inserted in the sleeve-shaped portion. The round corner of the insertion hole of the portion of the bonding attachment9in which the rebar2is inserted is pressed toward the center by the four dices91having an arc shaped grooves91a. In this manner, the pressed portion of the bonding attachment9is compressed and deforms, and the bonding attachment9is bonded to the rebar2.

In the embodiment, the bonding attachment9and the rebar2are also bonded with the granular fine powder disposed on the portion contacting each other by applying the application liquid mixed with the granular fine powder, before bonding, on the bonding attachment9or the rebar2. Further, the bonding attachment9can enhance the fixing force on concrete by the portion expanding toward the end.

The entire disclosure of the specification, the drawings, and the abstract included in Japanese Patent Application No. 2003-362703 filed Oct. 23, 2003 is hereby incorporated by reference.

REFERENCE SIGNS LIST