JP2012237118A - Precast concrete molding spacer and precast concrete molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily set a spacer for bringing a fiber sheet to a floated state within a mold form in order to ensure covering thickness of concrete and to also suppress the fiber sheet from being floated by piling concrete, in molding precast concrete with mesh-like fibers for peel prevention of concrete pieces as interior.SOLUTION: A precast concrete molding spacer 3 comprises a main body part 31 which is placed on a mesh-like fiber sheet 1, a plurality of leg parts 32 provided in a lower portion of the main body part 31 and spread over the mesh of the fiber sheet 1, and a reinforcing-bar holding part 33 which is assembled slidable in an upper portion of the main body part 31 for holding a reinforcing-bar 21 of a reinforcement cage 2. The leg parts 32 are spread over the mesh-like fiber sheet 1 laid within a mold form, the main body part 31 is placed on the fiber sheet 1 and while causing the reinforcing-bar holding part 33 to hold the reinforcing-bar 21 of the reinforcement cage 2 set within the mold form, concrete is piled within the mold form.

Description

  The present invention relates to a precast concrete molding spacer and a precast concrete molding method using the spacer.

For example, a precast concrete member such as a concrete segment used for a shield tunnel may be cracked or chipped due to temperature cracking, dry cracking, bumping or crushing from production to assembly. Further, after use, deterioration such as neutralization, salt damage, and alkali aggregate reaction proceeds. As a result, there is a risk that the covered concrete may be peeled off due to an increase in cracks and corrosion expansion of the reinforcing bars resulting therefrom.
Various measures against cracking and the prevention of peeling of floating concrete pieces by short fibers, sheets, and mesh-like synthetic fibers have been taken against the peeling phenomenon of the covered concrete.

Currently, there are the following three methods for preventing peeling using synthetic fibers.
1) Mix short fibers into concrete to prevent cracking.
2) A sheet-like fiber is affixed with an organic resin to suppress extrusion / falling of a covered concrete piece (see, for example, Patent Document 1).
3) A mesh-like fiber sheet is affixed with a cement-type material, or it is integrally wound with concrete near the surface to suppress extrusion / falling of the covered concrete piece (see, for example, Patent Document 2).

JP 2005-273388 A JP 2009-138402 A

  However, all methods still have problems with respect to the addition of material costs, an increase in manufacturing processes, reliability of the peeling prevention effect, and the like.

By the way, when setting a fiber sheet in precast concrete with predetermined covering thickness, it is necessary to set a fiber sheet in the state floated in a formwork in order to ensure covering thickness.
Thus, for example, it is conceivable to use a spacer as in Patent Document 2.
However, the spacer is tied to the lower surface of the fiber sheet using a binding wire, and the binding wire is tied to a further reinforcing bar at a necessary location.
Therefore, not only the setting of the spacer and the binding wire is troublesome, but also the fiber sheet is generally lighter than the concrete, so that there is a concern that the fiber sheet may be lifted by placing concrete.

  An object of the present invention is to easily set a spacer that floats a fiber sheet in precast concrete, and to prevent the fiber sheet from being lifted by placing concrete.

  In order to solve the above-described problems, the invention according to claim 1 includes a main body portion placed on a mesh-like fiber sheet, and a plurality of foot portions provided at a lower portion of the main body portion and straddling the mesh of the fiber sheet. And a reinforcing bar gripping part that is slidably assembled to the upper part of the main body part and holds the reinforcing bar of the reinforcing bar rod.

  A second aspect of the present invention is the precast concrete molding spacer according to the first aspect, wherein the reinforcing bar gripping portion is slidably assembled along a rail provided on the upper portion of the main body portion. And

  In the invention according to claim 3, the mesh of the mesh-like fiber sheet laid in the formwork straddles the foot of the precast concrete molding spacer according to claim 1 or 2, and the fiber A precast concrete molding method of placing the main body on a sheet and placing concrete in the formwork in a state where the rebar gripping part is grasped by a rebar of a reinforcing bar set in the formwork It is characterized by.

  A fourth aspect of the present invention is the precast concrete forming method according to the third aspect, wherein the position adjustment of the spacer with respect to the rebar is performed by sliding the rebar holding portion.

  According to the present invention, it is possible to easily set the spacer that makes the fiber sheet float a predetermined amount in the concrete, and it is also possible to suppress the fiber sheet from being lifted up by placing concrete.

BRIEF DESCRIPTION OF THE DRAWINGS The structure of one Embodiment to which the precast concrete shaping | molding method of this invention is applied is shown, and it is the perspective view which showed the fiber sheet set in a formwork, a reinforcing rod, and a spacer. It is an enlarged view of the spacer of FIG. It is a bottom view of the spacer part of FIG. It is a figure which shows the bend-up shape formed in the peripheral part of the fiber sheet of FIG.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
(Embodiment)
FIG. 1 shows a fiber sheet 1, a reinforcing bar 2 and a spacer 3 set in a mold as a configuration of an embodiment to which the precast concrete molding method of the present invention is applied.

  As shown in the figure, a mesh-like fiber sheet 1 is laid in a mold (not shown), and a reinforcing bar 2 is provided above the mesh sheet. A spacer is provided between the fiber sheet 1 and the reinforcing bar 2. 3 is provided. The spacer 3 is placed on the fiber sheet 1 and grips the reinforcing bar 21 below the reinforcing bar 2.

Here, as the fiber used for the fiber sheet 1, for example, vinylon resin or the like having a specific gravity as small as about 1.30 so as to float in the concrete and having good alkali resistance and cement-based adhesion is selected.
The size of the mesh of the fiber sheet 1 is about 10 × 10 to 20 × 20 mm from the viewpoint of ensuring that the concrete wraps around the front surface of the fiber sheet 1 and reducing the size of the concrete strip.
Give the fiber wire a little rigidity to prevent wrinkles and slack.
In the illustrated example, a biaxial mesh is used.

  In the above, in order to fit the fiber sheet 1 in a predetermined covering (3 to 10 mm is appropriate from the test), the spacers 3 are installed at an appropriate density between the formwork and the reinforcing bar rod.

  FIG. 2 is an enlarged view of the spacer 3, wherein 31 is a main body portion, 32 is a foot portion, 33 is a reinforcing bar gripping portion, and 34 is a rail.

  The spacer 3 is a mortar molding that has been used a lot, and as shown in the figure, four legs 32 are integrally formed on the lower surface of the cylindrical main body 31 at equal intervals in the circumferential direction. A metal rebar holding portion 33 is slidably assembled on the upper surface. In other words, a bifurcated rebar holding portion 33 for holding a reinforcing bar is slidably assembled along the lower surface of a pair of metal rails 34 fixed to the upper surface of the main body 31.

  FIG. 3 shows the spacer 3 portion of FIG. 1 from the bottom. As shown in the figure, the four legs 32 of the spacer 3 are straddled over the mesh of the fiber sheet 1 laid in the mold. The main body 31 is placed on the fiber sheet 1.

  Further, as shown in FIG. 2, the rebar 21 in the lower part of the reinforcing bar 2 set in the mold is held in a state where the bifurcated rebar holding part 33 on the main body 31 is held. As a result, the fiber sheet 1 is suppressed by the weight of the reinforcing bar 2 through the spacer 3 to be lifted by the hydraulic pressure of the concrete placed in the mold.

  In addition, the position of the spacer 3 with respect to the reinforcing bar 21 is adjusted by sliding the reinforcing bar gripping part 33 along the rail 34 on the main body 31, and the position of the mesh of the fiber sheet 1 and the reinforcing bar 21 of the reinforcing bar 2. Absorbs misalignment.

  FIG. 4 shows the shape of the bent-up part 11 formed in the peripheral part of the fiber sheet 1 of FIG.

  That is, most of the concrete peeling phenomenon occurs at the end of the member, and as shown in the drawing, the peripheral portion of the fiber sheet 1 is formed as a bent-up portion 11 bent inward along the mold. Keep it.

When molding the concrete segment, the fiber sheet 1 is first laid in the mold.
Next, an appropriate number of spacers 3 are placed across the mesh of the fiber sheet 1.
Next, the reinforcing bar 2 is stored.
Then, the reinforcing bar 21 on the lower part of the reinforcing bar rod 2 is caused to hold the bifurcated reinforcing bar holding part 33 on the spacer 3. At that time, the displacement of the mesh of the fiber sheet 1 and the reinforcing bar 21 of the reinforcing bar 2 is absorbed by the sliding movement of the reinforcing bar gripping part 33 along the rail 34 above the spacer 3.
After that, concrete is laid.

As described above, according to the concrete segment forming of the embodiment, the spacer 3 for securing the covering thickness of the concrete is placed on the fiber sheet 1 across the mesh, and the reinforcing bar gripping portion 33 is gripped by the reinforcing bar 21 of the reinforcing bar 2. By doing so, the spacer 3 can be easily set.
And it can suppress by the weight of the reinforcing bar 2 through the spacer 3, and can also suppress the lifting of the fiber sheet 1 by concrete placement.
Therefore, the mesh-like fiber sheet 1 can be integrally wound with the concrete near the surface to prevent the covering concrete pieces from peeling off.

(Modification)
In the above-described embodiment, the concrete segment is used. However, the present invention is not limited to this, and may be other precast concrete in which concrete pieces such as concrete beams may be peeled off.
In the embodiment, a biaxial mesh is used, but a uniaxial triaxial mesh may be used.
Furthermore, the type of fiber, the material and shape of the spacer (main body, foot, and reinforcing bar gripping part), the number of legs, the sliding structure of the reinforcing bar gripping part, etc. are arbitrary, and other specific details such as the detailed structure Of course, it can be changed appropriately.

DESCRIPTION OF SYMBOLS 1 Fiber sheet 11 Bending part 2 Reinforcement rod 21 Reinforcing bar 3 Spacer 31 Main body part 32 Foot part 33 Reinforcing bar holding part 34 Rail

Claims (4)

A main body placed on a mesh-like fiber sheet;
A plurality of foot portions provided at a lower portion of the main body portion and straddling the mesh of the fiber sheet;
A precast concrete molding spacer comprising: a reinforcing bar gripping part that is slidably assembled to the upper part of the main body part and holds the reinforcing bar of the reinforcing bar rod.   2. The precast concrete molding spacer according to claim 1, wherein the reinforcing bar gripping part is slidably assembled along a rail provided on the upper part of the main body part. The main body is placed on the fiber sheet, straddling the foot portion of the precast concrete molding spacer according to claim 1 or 2 on a mesh of a mesh-like fiber sheet laid in a mold. With
In a state where the reinforcing bar gripping part is gripped by a reinforcing bar of the reinforcing bar set in the mold,
A precast concrete molding method, wherein concrete is placed in the mold.   The precast concrete forming method according to claim 3, wherein the position adjustment of the spacer with respect to the reinforcing bar is performed by sliding the reinforcing bar holding part.

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