JP2017197934A - Spray concrete construction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spray concrete construction method which can simply form a concrete structure functioning stably and for a long time and having a longer life period.SOLUTION: A spray concrete construction method covers a natural ground of a slope with a concrete structure by a series of steps for stabilization and comprises a primary spray step of spraying discontinuous fiber-mixed concrete on a slope to be hardened so as to form a displacement absorption layer, a displacement absorption step of generating an initial crack due to displacement of a natural ground in the displacement absorption layer, and a secondary spray step of spraying discontinuous fiber-mixed concrete on the surface of the displacement absorption layer to be hardened so as to form a restraining layer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a concrete spraying method, and more particularly to a concrete spraying method capable of easily forming a concrete structure that functions stably for a long period of time.
In the following specification and claims, “concrete” is used in the meaning including mortar.

The concrete spraying method stabilizes the slope by spraying concrete onto the ground of the slope and sealing the slope with a concrete structure to prevent erosion, weathering, infiltration of outside air and rainwater, etc. that cause the slope collapse. For the purpose. The concrete spraying method is widely used because it is excellent in workability, has a very high shielding effect against outside air, temperature change, permeated water, etc., and is economical.
As a conventional technique related to the concrete spraying method, for example, there are methods as disclosed in Patent Documents 1 and 2.

JP-A-11-36316 JP-A-5-321267

The conventional concrete spraying method has the following problems.
<1> The formed concrete structure is thin and has a large surface area. In addition, when the ground surface of the slope is uneven, it is difficult to manage the spray thickness, and the layer thickness tends to vary. For this reason, initial cracks (cracks) are likely to occur in the surface layer of the concrete structure due to factors such as displacement of the natural ground, vibration, and drying shrinkage.
<2> Since the construction is performed on an inclined surface, the concrete is sag due to its own weight during curing, and cracks due to this tend to occur.
<3> Generally, a PVC pipe is installed in the natural ground in order to discharge osmotic water or spring water. For this reason, stress concentrates around the PVC pipe and cracks occur (Fig. 5), or weathered earth and sand flows out of the PVC pipe, thereby forming a cavity inside the structure. is there.
<4> Since general curing cannot be performed, it is directly affected by the external environment such as temperature change, wind and rain, drying and freezing, and cracking due to drying and freezing is likely to occur.

FIG. 6 is an example of a crack generated in a concrete structure. This crack deeply reaches the natural ground (note that the three vertical holes along the crack are core holes for investigating the cause).
These initial cracks have a great influence on the subsequent deterioration and acceleration of the concrete structure.
That is, rainwater, chlorides, air pollutants, etc. that have entered from the opening of the initial crack deteriorate the concrete structure, weather the ground, and corrode the wire mesh in the structure. In addition, the water that has entered the structure freezes, causing a lack of adhesion to the ground and an internal cavity, which may cause the structure to peel off or peel off.
Thus, since the concrete structure by the conventional spraying method deteriorates and deteriorates in 10 to 20 years or more, there is a concern about the peeling of concrete pieces.

  An object of the present invention is to provide a concrete spraying method that solves these problems of the prior art.

  The concrete spraying method of the present invention for solving the above-mentioned problems is a concrete spraying method in which the ground of the slope is covered with a concrete structure and stabilized by a series of steps, and the short fiber is applied to the slope. The primary spraying process, which forms the displacement absorption layer by spraying the concrete mixed with, the displacement absorption process, which causes the initial cracking due to the displacement of the ground in the displacement absorption layer, and the surface of the displacement absorption layer A secondary spraying step in which concrete mixed with short fibers is sprayed and cured to form a constrained layer.

  In the concrete spraying method of the present invention, the displacement absorbing layer is left as it is for 72 hours or more after curing when the concrete in the primary spraying process is ordinary concrete, and for 24 hours or more after curing when the concrete is early-strength concrete. You may do it.

  The concrete spraying method of this invention may have the process of apply | coating a synthetic resin primer to the whole surface of a displacement absorption layer before a secondary spraying process.

  The concrete spraying method of the present invention may have a step of stretching a wire mesh over the entire surface of the displacement absorbing layer before the secondary spraying step.

  The concrete spraying method of the present invention may have a step of laying a drainage mat on the slope before the primary spraying step.

  The concrete spraying method of the present invention may include a step of applying a silane / siloxane-based permeable water absorption inhibitor to the entire surface of the constraining layer after the secondary spraying step.

  In the concrete spraying method of the present invention, the displacement absorbing layer may be made of early-strength concrete, and the constraining layer may be made of ordinary concrete.

Since the concrete spraying method of the present invention has the above configuration, it has the following effects.
<1> After generating an initial crack in the displacement absorbing layer due to displacement and vibration of the natural ground, the displacement absorbing layer is covered with the constraining layer together with the crack. For this reason, generation | occurrence | production of the initial stage crack to a structure surface can be prevented.
<2> Since a short fiber mixed concrete is used, a stable concrete structure with high toughness can be formed. As a result, it is possible to prevent the occurrence of initial cracks due to drying shrinkage and sagging of the material.
<3> Prior to spraying the constraining layer, the surface of the cracked displacement absorbing layer is coated with a synthetic resin primer to fill and seal the cracks in the displacement absorbing layer and to bond the displacement absorbing layer to the constraining layer. Can be made into an integrated structure.
<4> By applying a silane / siloxane water absorption inhibitor on the surface of the constraining layer, it is possible to prevent moisture and chloride from entering and prevent frost damage.
<5> By laying a drain mat in the ground instead of the conventional drain pipe, it prevents the occurrence of cavities due to the outflow of the back ground, and prevents the occurrence of cracks due to stress concentration on the drain pipe. Can do.
<6> From the above <1> to <5>, a concrete structure having a long service life that functions stably for a long period of time can be easily formed by the spraying method, and the occurrence of peeling and peeling can be prevented.

Explanatory drawing of the concrete spraying construction method which concerns on this invention. The flowchart of the concrete spraying construction method which concerns on this invention. The flowchart of the other Example of the concrete spraying construction method which concerns on this invention. The drawing substitute photograph which shows the state after construction of the concrete spraying construction method which concerns on this invention. The drawing substitute photograph which shows the state which the crack generate | occur | produced around the PVC pipe in the prior art. A drawing-substituting photograph showing a state in which a deep crack reaching a natural ground has occurred in the prior art.

  Hereinafter, the concrete spraying method of the present invention will be described in detail with reference to the drawings.

[Concrete spraying method]
<1> Overall configuration (FIGS. 1 and 2).
The concrete spraying method according to the present invention includes a displacement absorbing layer 10 and a constraining layer on the slope A by continuously performing a first spraying process, a displacement absorbing process, a primer applying process, and a second spraying process. It is a construction method for forming a concrete structure 1 having 20 two-layer structures.
The reason why the concrete structure 1 has a two-layer structure is that an initial crack is generated in the displacement absorbing layer 10 which is the first layer due to displacement and vibration of the ground, and this displacement absorbing layer 10 is covered with the constraining layer 20 together with the crack. This is to prevent the occurrence of initial cracks on the surface of the concrete structure 1.
In addition, the concrete spraying method of this invention is a construction method which covers and stabilizes the natural ground of the slope A with the concrete structure 1 by a series of continuous processes.
Accordingly, a method of spraying concrete on the surface of an existing concrete structure where cracks have occurred for the purpose of reinforcement or repair is out of the scope of the present invention.

<1.1> Short fiber mixed concrete.
In the concrete spraying method of the present invention, short fiber mixed concrete is used for spraying.
As the concrete, a concrete having a general composition using ordinary Portland cement is used. However, the present invention is not limited to this, and a known cement or blend such as early-strength Portland cement may be used depending on the construction situation.
The short fiber is a synthetic resin short fiber. Specifically, short fibers such as nylon, vinylon, and polypropylene can be used. However, the present invention is not limited to this, and steel fibers (steel fibers), carbon fibers (carbon fibers), and the like may be employed.
The length and the material diameter of the short fiber are appropriate. For example, when short fibers having a length of about 10 to 50 mm and a material diameter of about 0.1 to 2.0 mm are employed, sufficient toughness is imparted to the concrete structure 1. Can do. Moreover, if the short fiber which provided the unevenness | corrugation and protrusion on the surface is employ | adopted, a restraint force can be raised more.
These short fibers are mixed with concrete in an amount of about 0.5 VOL% to 2.0 VOL% to produce a short fiber mixed concrete.

<2> Primary spraying process.
The primary spraying process is a process of forming the displacement absorbing layer 10 by spraying the short fiber mixed concrete on the slope A and curing it.
Prior to spraying, the slope A is cleaned to remove root stumps, floats, earth and sand, etc., which prevent the sprayed concrete from adhering to the slope A.
Subsequently, the short fiber mixed concrete is sprayed to a desired thickness. The spraying thickness is about half of the layer thickness of the entire concrete structure 1.
After spraying, the sprayed concrete is cured through a predetermined period, and the displacement absorbing layer 10 is formed.

<3> Displacement absorption process.
The displacement absorbing step is a step of causing the initial cracking caused by the displacement / vibration of the natural ground and the site conditions in the displacement absorbing layer 10.
The displacement absorbing step is performed by leaving the displacement absorbing layer 10 for a certain period until the next step. The certain period is a period sufficient to cause initial cracks on the surface of the displacement absorbing layer 10.
Although the specific period varies depending on the environment and season, in the case of ordinary concrete, the displacement absorbing layer 10 is allowed to stand for 72 hours or more after the concrete is cured. In the case of early-strength concrete, it is allowed to stand for 24 hours or more after the concrete is cured.
Here, “early-strength concrete” refers to concrete using early-strength Portland cement, or concrete mixed with a curing accelerator as an admixture, and “ordinary concrete” refers to a general blend using ordinary Portland cement. Point to concrete. “Hardening” refers to the time when the concrete has set (JIS A 1147).

<4> Primer application step.
Prior to the secondary spraying process, the primer 40 is applied to the entire surface of the displacement absorbing layer 10. The primer 40 may be sprayed.
In this example, a synthetic resin primer is employed as the primer 40. However, the present invention is not limited to this, and other known various primers may be employed.
By applying the primer 40 to the surface of the displacement absorbing layer 10, the adhesion strength between the displacement absorbing layer 10 and the constraining layer 20 described later can be increased, and both can be integrated.
In addition, by filling the initial crack generated in the displacement absorbing layer 10 with the primer 40, the water absorption of the cracked portion is blocked and a sealing effect is imparted, and the occurrence of cracks due to rapid drying shrinkage of the constraining layer 20 can be suppressed. .

<5> Secondary spraying step.
The secondary spraying process is a process of forming the constraining layer 20 by spraying and curing the short fiber mixed concrete on the surface of the displacement absorbing layer 10.
Short fiber mixed concrete is sprayed onto the surface of the displacement absorbing layer 10 coated with the primer 40 to a thickness equivalent to that of the displacement absorbing layer 10.
After spraying, the sprayed concrete is cured through a predetermined period, and the constraining layer 20 is formed. Thereby, the concrete structure 1 is completed.

<6> Features of this method.
The present invention provides a concrete spraying method in which (1) the concrete structure 1 has a two-layer structure including a displacement absorbing layer 10 and a constraining layer 20, and (2) displacement absorption before the secondary spraying step. By providing the step, the initial cracking is intentionally induced in the displacement absorbing layer 10, (3) Prior to the spraying of the constraining layer 20, the synthetic resin primer 40 is applied to the surface of the displacement absorbing layer 10 to displace it. It is characterized by enhancing the adhesion strength between the absorbent layer 10 and the constraining layer 20 and sealing cracks of the displacement absorbing layer 10 and (4) imparting toughness to the concrete structure 1 by using short fiber mixed concrete. Have
Conventionally, two-stage spraying has been considered undesirable because of the problem of adhesion between the first layer and the second layer. Therefore, when the spraying is completed once or when it is performed twice, the second layer is sprayed as soon as possible before the first layer is cured.
On the other hand, the concrete spraying method of the present invention dares to make the concrete structure 1 have a two-layer structure, harden the displacement absorbing layer 10 by the primary spraying process, and then perform the displacement absorbing process before constructing the secondary spraying process. This is a method of causing the displacement absorbing layer 10 to absorb the displacement of the natural ground by causing the initial cracking in the displacement absorbing layer 10 through the interposition of.
By covering the displacement absorbing layer 10 after the initial cracking with the constraining layer 20 together with the cracks, cracks due to the location conditions of the construction surface, that is, unevenness of the natural ground, vibration, expansion, subsidence, sand-absorbing geology such as mudstone, etc. Initial cracks due to rapid drying and the like, and initial cracks due to the influence of natural ground can be absorbed, and long-term cracks due to drying shrinkage after curing can be suppressed by the short fibers of the constrained layer 20.
In addition, in order to avoid poor adhesion between the displacement absorbing layer 10 and the constraining layer 20 due to the two-stage spraying, the synthetic resin primer 40 is applied to the surface of the displacement absorbing layer 10 prior to the secondary spraying, and is generated in the displacement absorbing layer 10. The cracks are sealed and the adhesive force with the constraining layer 20 is increased to form an integrated structure.
By combining these features, it is possible to easily form the concrete structure 1 that has shear resistance, prevents the occurrence of peeling and peeling, and functions stably for a long period of time by the spraying method.

<7> State after construction.
FIG. 4 is a drawing-substituting photograph showing the concrete structure 1 after 180 days from the execution of the concrete spraying method according to the present invention.
In the concrete spraying method, drying and long-term shrinkage of the sprayed surface end about 90 days after construction.
On the other hand, the concrete structure 1 shown in FIG. 4 has no cracks on the surface of the constraining layer 20 even after 180 days from the construction.
From the above, the effectiveness of the concrete spraying method according to the present invention can be seen.

[Example of installing a wire mesh on the displacement absorbing layer]
Next, another embodiment in which a metal mesh is stretched on the displacement absorbing layer will be described.
In this example, it has the process of extending the wire mesh 30 on the surface of the displacement absorption layer 10 after a primer application process (FIG. 3).
The wire mesh 30 employs a rhombus wire mesh that easily follows the unevenness of the slope A. However, the present invention is not limited to this, and a welded wire mesh may be adopted.
The wire mesh 30 is stretched so as to be in close contact with the entire surface of the displacement absorbing layer 10 to which the primer 40 is applied, and important points are fixed to the displacement absorbing layer 10 with anchor pins 70.
Subsequently, a secondary spraying process is performed from above the wire mesh 30 of the displacement absorbing layer 10.
In this example, the wire mesh 30 facilitates the attachment of the shotcrete to the displacement absorbing layer 10, and the integrity of both the displacement absorbing layer 10 and the constraining layer 20 can be further enhanced.
Moreover, even when the slope A has a steep slope, it is possible to prevent the shotcrete from sagging or peeling off.

[Example of drainage mat laid on the slope]
Next, another embodiment in which a drain mat is laid on the slope will be described.
When there is spring water from the slope A to be constructed, the hydration reaction of the concrete is hindered, and internal voids and cracks may occur. In this case, the quality of the concrete structure 1 is lowered, and the adhesion between the concrete and the natural ground is lowered.
Further, in order to prevent this, generally, one drain pipe is provided at 4 m ² . However, this drainage pipe is not necessarily installed at the location of the spring, and it not only causes the earth and sand of the natural ground to flow out and creates a cavity on the back, but also causes cracks due to stress concentration in the drainage pipe portion of the concrete structure 1. (Fig. 5).
Therefore, in this example, prior to the primary spraying process, there is a process of laying the drainage mat 50 on the slope A (FIG. 3).
Specifically, first, a strip-shaped vertical drainage mat 51 is laid at a predetermined interval, for example, a pitch of 1.5 m, on a slope A with spring water, and fixed with an anchor or the like.
Subsequently, the oblique drainage mat 52 is connected to both sides of the vertical drainage mat 51 so that the lower end portion is connected to the body of the vertical drainage mat 51. That is, the drain mat 50 is laid on the slope A in a downward arrow shape.
And a primary spraying process is implemented from on this drainage mat 50 laid.
In this example, the spring water generated from the slope A is smoothly discharged to the outside of the concrete structure 1 through the drainage mat 50. Therefore, it is possible to prevent quality deterioration of the concrete structure 1 and generation of internal voids.
Moreover, since the drain pipe is not used, the occurrence of cracks in the concrete structure 1 due to stress concentration can be prevented.

[Example of applying a water absorption inhibitor to the constraining layer]
Next, another embodiment in which a water absorption inhibitor is applied to the constraining layer will be described.
In this example, after the secondary spraying step, the surface of the constraining layer 20 has a step of coating the entire surface with a silane / siloxane water absorption inhibitor 60 as a concrete protective material (FIG. 3).
Accordingly, it is possible to suppress water intrusion into the concrete structure 1, suppress alkali aggregate reaction, and extend the life of the concrete structure 1.

[Examples of spraying different concrete in the primary spraying process and the secondary spraying process]
Next, another embodiment in which different concrete is sprayed in the primary spraying process and the secondary spraying process will be described.
In this example, in the primary spraying process, the early-strength concrete is sprayed onto the slope A to form the displacement absorbing layer 10. On the other hand, in the secondary spraying process, the concrete is sprayed onto the displacement absorbing layer 10 to form the constraining layer 20.
In this way, cracks are induced in the displacement absorbing layer 10 at an early stage, and the waiting time until the secondary spraying process is shortened, while the displacement absorbing layer 10 is restrained by the constraining layer 20 made of ordinary concrete which is not easily cracked. Thus, the strength of the entire structure can be ensured.
Therefore, it is possible to achieve both the construction efficiency and the stability of the structure.

DESCRIPTION OF SYMBOLS 1 Concrete structure 10 Displacement absorption layer 20 Constrained layer 30 Wire mesh 40 Primer 50 Drainage mat 51 Vertical drainage mat 52 Diagonal drainage mat 60 Water absorption inhibitor 70 Anchor pin A Slope c Crack

Claims (7)

A concrete spraying method that stabilizes the natural ground of the slope by covering it with a concrete structure through a series of processes,
A primary spraying step of spraying and curing concrete mixed with short fibers on the slope to form a displacement absorbing layer;
A displacement absorbing step for causing an initial crack in the displacement absorbing layer due to displacement of a natural ground; and
A secondary spraying step of spraying and curing concrete mixed with short fibers on the surface of the displacement absorbing layer to form a constrained layer, and
Concrete spraying method.   The displacement absorbing step is performed by leaving the displacement absorbing layer for 72 hours or more after curing when the concrete in the primary spraying step is ordinary concrete, and for 24 hours or more after curing when the concrete is early strength concrete. The concrete spraying method according to claim 1, characterized in that it is characterized.   The concrete spraying method according to claim 1, further comprising a step of applying a synthetic resin primer to the entire surface of the displacement absorbing layer before the secondary spraying step.   The concrete spraying method according to claim 1, further comprising a step of stretching a wire mesh over the entire surface of the displacement absorbing layer before the secondary spraying step.   The concrete spraying method according to claim 1, further comprising a step of laying a drainage mat on the slope before the primary spraying step.   The concrete spraying method according to claim 1, further comprising a step of applying a silane / siloxane-based permeable water absorption inhibitor to the entire surface of the constraining layer after the secondary spraying step.   The concrete spraying method according to claim 1, wherein the displacement absorbing layer is made of early-strength concrete, and the constraining layer is made of ordinary concrete.