JPH0651979B2 - Reverse winding concrete method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reverse-winding concrete construction method in which concrete is sequentially placed from the upper part to the lower part, and particularly, a post-cast concrete is firmly bonded to a lower surface of the precast concrete. Regarding the technology to make.

<< Conventional Technology >> In the reverse-rolling concrete method, it is difficult to bring the post-cast concrete in the lower part into close contact with the pre-cast concrete in the upper part. Therefore, most of the reverse winding methods to date have dealt with such problems by injecting grout after hardening of concrete into the gap formed in the spliced portion or filling the gap with non-shrink mortar. This is a measure to fill the gap created in the splice section with post-processing.

In addition, recently, various techniques for preventing a gap from being formed in the splice portion have been proposed. For example, it is constructed by using expansive concrete, and its expansiveness prevents a gap from being formed in the joint. In addition, the poured post-cast concrete is hardened while being pressed to prevent the post-cast concrete from sinking so that no gap is generated.

As a technique to be used in combination with the above-mentioned measures to fill the gaps in the joints by post-treatment or to prevent the gaps from forming in the joints, by roughening the lower surface of the precast concrete, There are ways to increase the bond strength of.

As a roughening method of the lower surface of the precast concrete, there are methods such as rubbing strongly with a wire brush, washing with water after sandblasting, applying a settling retarder to the lower surface portion during pouring, and washing with water after demolding. Known from the past. The simple method has a problem that the work efficiency is remarkably inferior, and the method using the sand blast requires a large-scale facility and the work environment is remarkably deteriorated. Therefore, the use of a setting retarder is considered to be an effective method.

The conventional roughening method of the lower surface of the precast concrete using a setting retarder will be described in detail. First, a liquid setting retarder is applied to the upper surface of the outer formwork that partitions the lower surface of the concrete pouring space, and concrete is poured onto this. Then, the set retarder acts on the bottom surface of the poured concrete, and the hardening of this part is delayed. Then, when the lower surface of the cast concrete is washed with high pressure water after the mold is removed, the uncured concrete is removed and a rough and rough concrete surface appears.

<Problems to be Solved by the Invention> As described above, the conventional roughening method in which a liquid setting retarder is applied to the upper surface side of the bottom mold and concrete is placed in the conventional roughening method has the following problems. It was

The work of uniformly applying the setting retarder to the bottom mold is troublesome. If it is not applied uniformly, there will be large unevenness in the depth of action of the retarder.

When concrete is placed on the bottom formwork coated with retarder, the retarder disperses due to the momentum, and even if it is applied uniformly, the distribution of retarder is extremely disturbed. To be done.

The bottom formwork is not installed horizontally, but is installed tilted with the foreground raised. A setting agent is applied on the inclined bottom formwork and concrete is poured, but the liquid retarder collects on the lower side along the inclination. As a result, there is a shortage of coagulant on the high side and too much retarder on the low side.

As described above, it is difficult to uniformly apply the setting retarder to the lower surface of the cast concrete by the conventional method, and the rough surface does not appear due to the lack of the retarder, or the retarder acts deeper than necessary. During washing with water, a large amount of uncured concrete locally flowed out, and a uniform roughening effect could not be obtained.

In addition to the above, there was the following problem. In a general reverse-rolling concrete construction method, ordinary concrete using ordinary aggregate such as sand, gravel, or crushed stone is used. In the case of concrete using such granular small ordinary aggregate, even if the lower surface of the precast concrete is roughened by the method using the above-mentioned set retarder, the degree of unevenness is not so large and it is roughened. Although the bond strength with the post-cast concrete was higher than that of the case without the above, the effect was not sufficient to meet the expectations.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to firmly bond the lower surface of the precast concrete and the postcast concrete with a simple work.

<< Means for Solving the Problem >> Therefore, in the present invention, a sheet impregnated with a setting retarder is joined to the upper surface side of the bottom formwork, and at least a portion in contact with the sheet is provided with fiber reinforced concrete. After removing the mold, the lower surface of the fiber reinforced concrete on which the sheet had been hit was washed with water to expose the fibers, and the lower concrete to be placed next was joined to the exposed surface of the fibers.

<< Action >> The above sheet is uniformly impregnated with a set retarder in advance, and its distribution is completely unaffected by the inclination of the bottom formwork or the momentum of the placed concrete, and the set retarder is evenly distributed on the lower surface of the placed concrete. Of action.

Further, since the portion roughened by the action of the setting retarder is the fiber-reinforced concrete, the fibers are exposed in the roughened portion. Since the post-cast concrete adheres to the exposed surface of the fiber, the reinforcing effect of the fiber is also exerted at this joint portion.

Example When carrying out the method of the present invention, a sheet made of paper, non-woven fabric, polymeric water-absorbing material or the like, which is previously impregnated with a setting retarder, is used. As this type of sheet, "SKP Zerviment" (trade name) is commercially available.

As shown in FIG. 1, the retarder-impregnated sheet 2 described above is placed on the upper surface side of the bottom mold 1 and is fixed by, for example, a staple fitting 3. Next, as shown in FIG. 2, the bottom formwork 1 with the sheet 2 and the side formwork 5 are installed in predetermined portions of the earth retaining wall 4, and concrete is poured into the concrete placing space surrounded by these. Here, first, an appropriate amount of fiber-reinforced concrete 6 is poured, and then ordinary concrete 7 is poured. The first fiber-reinforced concrete 6 poured into contact with the sheet 2 on the bottom mold 1, and ordinary concrete 7 is placed on the layer of this concrete 6. Steel fibers, vinylon fibers, polypropylene fibers, carbon fibers and the like are used as reinforcing fibers for the concrete 6, and steel fibers having high hardness are particularly preferable. The ordinary concrete 7 is concrete using ordinary aggregate such as sand, gravel, or crushed stone.

When the fiber-reinforced concrete 6 touches the sheet 2 on the bottom mold 1, the set retarder impregnated in the sheet 2 is eluted into the concrete 6 by the moisture contained in the concrete 6. As a result, the portion of the fiber reinforced concrete 6 that is in contact with the sheet 2 is delayed in curing as compared with other portions. After the fiber-reinforced concrete 6 and the ordinary concrete 7 are hardened, the bottom formwork 1 and the side formwork 5 are removed, and water is sprayed onto the lower surface of the fiber-reinforced concrete 6 which is in contact with the sheet 2 as shown in FIG. And wash away the uncured surface concrete.

Then, as shown in FIG. 4, the reinforcing fibers 6a are exposed on the lower surface of the concrete 6 and the concrete surface becomes a rough surface. Since the action of the setting retarder by the sheet 2 is evenly applied to the concrete 6, the surface state of the lower surface of the concrete 6 (the degree of unevenness and the exposed state of the reinforcing fiber 6a) is almost entirely uniform.

After this, post-cast concrete is placed in the lower part of the concrete 6 in the same manner, but when the post-cast concrete is spliced on the lower surface of the pre-cast concrete where the reinforcement fibers 6a are exposed and uneven, the exposure of the reinforcement fibers 6a The part penetrates into the post-cast concrete and the bondability of this joint is extremely high.

In addition, when the curing period of the concrete is extended, the hardness of the concrete becomes large, so it is better to use high-pressure water in the above-mentioned washing step. Further, the fiber-reinforced concrete may be used not only locally but entirely.

<Effects of the Invention> As described in detail above, in the reverse winding concrete construction method according to the present invention, a sheet impregnated with a setting retarder is joined to the upper surface side of the bottom formwork, and the fiber-reinforced concrete is placed thereon. Since the retarding agent contained in the sheet is dissolved and acts evenly on the lower surface of the cast concrete, the lower surface of the cast concrete that was hit by the above-mentioned sheet was washed with water after demolding. The uneven surface where the reinforcing fibers are exposed appears uniformly over the entire area. Since the post-cast concrete is spliced to the exposed uneven surface of the reinforcing fiber, the bonding force of the spliced portion becomes extremely large.

[Brief description of drawings]

1 to 4 are diagrams showing schematic steps of a reverse winding concrete construction method according to an embodiment of the present invention. 1 ... Bottom formwork, 2 ... Retarder impregnated sheet 3 ... Staple fittings, 4 ... Soil retaining wall 5 ... Side formwork 6 ... Fiber reinforced concrete 6a ... Reinforcing fiber, 7 ... Ordinary concrete

Claims (1)

[Claims] 1. A reverse winding concrete construction method in which concrete is sequentially poured from the upper part to the lower part, and a sheet impregnated with a setting retarder is joined to the upper surface side of a bottom formwork for partitioning the lower surface of the concrete pouring space. Place the fiber reinforced concrete in at least the part in contact with this sheet, and after removing the mold, wash the bottom surface of the fiber reinforced concrete with water to expose the fibers and then place the fiber on the exposed surface. Reverse-rolling concrete method characterized by joining lower concrete to be joined.