JPH01310062A - Placing method for new concrete jointed to underside of existing concrete structure - Google Patents

Abstract

PURPOSE:To strengthen the adhesion of concrete at a joint surface by arranging the upper end of a formwork via a small gap from the underside of concrete and pressing concrete containing a separation reducing agent and a swelling agent into the formwork via the concrete placing opening thereof. CONSTITUTION:When a division 14 is built between the first basement slab 10 and the second basement slab 12, for example, a reinforcement 16 is assembled and the upper end thereof is embedded in the slab 10 for connection to an anchor 18. Also, a swelling agent, a separation reducing agent and the like are added to jointing concrete. Thereafter, a pair of formworks 20 having a concrete placing opening 22 and a drain hole 2 is set at the outside of the reinforcement 16, and a small interval 28 is formed between the upper ends of formworks 20 and the slab 10. Then, the concrete after placed via the opening 22, is pressurized with a pump at an area reaching the underside of the slab 10. In addition, the concrete is kept under pressure due to the effect of the swelling agent until cured.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for placing new concrete that is jointly formed on the underside of an existing concrete structure, and in particular, to a method for placing new concrete that is jointly formed on the underside of an existing concrete structure. This invention relates to a pouring method that can improve surface integrity.

(Prior art) As is well known, when adding a space such as a basement or parking lot to the basement of an existing building structure, new concrete structures such as walls are cemented onto the underside of the existing concrete structure. be done.

Figure 4 shows a general method for forming pour joints in newly constructed concrete structures in such cases.

In the method shown in the figure, a space is excavated below an existing concrete structure 1, reinforcing bars 2 are assembled, and a formwork 3 is erected around the outer periphery of the reinforcing bars 2.

In the formwork 3 to be constructed here, a vibrator 4 is inserted in order to sufficiently fill the concrete to the bottom of the reinforcing bars 2.
In addition, it is installed at a fairly large distance from the lower surface of the existing concrete structure 1 so that its operation can be easily performed.

When the installation of the formwork 3 is completed, as shown in FIG. 4(b), concrete 1 and 6 are poured through the concrete supply hose 5, and the top surface of the poured concrete 6 is When near the upper end of the frame 3, pouring of concrete 6 is stopped and the formwork 3 is extended to the lower surface of the existing concrete structure 1.

Next, the concrete supply hose 5 is connected to the pouring lower provided above the formwork 3, and the concrete 6 is poured into the formwork 3.
A new concrete structure 8 is formed by pouring concrete 6 and removing the formwork 3 after the poured concrete 6 has hardened.

However, the joint surface between the new concrete structure 8 and the existing concrete structure 1 formed by such a method has the following technical problem.

(Problem to be Solved by the Invention) In other words, the concrete 6 poured in the formwork 3 generates breathing water during the curing period after pouring, and this rises to the pouring surface and intervenes, causing Concrete structure 1
A gap 9 was created between the concrete structure 8 and the new concrete structure 8, and strong integrity between the structures could not be obtained.

To solve this problem, epoxy resin or mortar is injected into the gap 9 to ensure the integrity of the structure, but this method takes a long time and
It is difficult to ensure sufficient adhesion strength on the joint surface.

Therefore, for example, it is possible to mix an expanding agent such as aluminum powder, which is used when constructing an underground tank using the reverse winding method, into the concrete 6, but the existing concrete structure 1 may be Since the lower surface is often flat, even if the poured concrete 6 expands due to the action of the expanding agent, the amount of expansion is small, so there is a problem that breathing water cannot be sufficiently removed from the joint surface.

On the other hand, one way to reduce breathing water is to harden the concrete. If this method is adopted, the poured concrete must be compacted, but if the wall thickness is thin and the reinforcement is dense, , it becomes difficult to perform sufficient compaction.

This invention was made in view of these conventional problems, and its purpose is to provide sufficient adhesion strength at the joint surface between existing and new concrete structures without compaction. The goal is to provide a method that can ensure that

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for placing new concrete that is jointly formed on the lower surface of an existing concrete structure. A formwork is provided with a concrete casting opening that can be opened and closed, and the upper end of the formwork is placed at a small distance from the lower surface of the existing concrete structure, and a separation reducing agent is passed through the casting opening.

The present invention is characterized in that concrete containing an expanding agent is press-fitted into the formwork until it reaches the lower surface of the existing concrete structure, and then the concrete pouring opening is closed.

(Function) According to the two-leg construction method for placing new concrete, concrete containing a separation-reducing agent and an expanding agent is press-fitted into the formwork, so it must be sufficiently distributed in the narrow space. At the same time, the generation of breathing water is suppressed, and strong integrity can be expected between the underside of the existing concrete structure and the new concrete.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIGS. 1 to 3 show an embodiment of the method of placing new concrete to be jointly formed on the lower surface of an existing concrete structure according to the present invention.

The method for placing new concrete shown in the same figure exemplifies the case where the present invention is applied to the expansion of a basement. Specifically, the concrete basement-floor slab 10 of an existing structure is
A second basement floor is constructed below, and the second basement floor is constructed by excavating the space below the basement floor slab 10 to form a space, and forming the second basement floor slab 12 at a distance from the basement floor slab 10. Then, the partition wall 14 is constructed between these slabs 10 and 12.

In this example, the existing concrete structure is the basement-story slab 10, and the concrete structure constructed by pouring new concrete is the partition wall 14.

The partition wall 14 is constructed by the method described below.

First, the reinforcing bars 16 buried in the partition wall 14 are assembled at the construction position of the partition wall 14, and their upper ends are connected to the basement-floor slab 1.
The retrofit embedded in 0 is connected to the anchor 18.

Once the reinforcing bars 16 have been assembled, a pair of formworks 20, 20 are installed on the outside thereof.

This formwork 20 is selected to have a rigidity capable of withstanding the press-fitting of concrete, which will be described later.
are provided on the upper side thereof, and the pouring port 22 and the discharge port 24 are each provided with an on-off valve 26. as shown in FIG.
26 is attached.

The formwork 20 is also erected so that a small gap 28 is formed along its entire length between its upper end and the lower surface of the basement-floor slab 10.

This small interval 28 is set, for example, to a value that does not allow the aggregate in the poured concrete to flow out.

When the erection of the formwork 20 is completed as described above, the concrete supply hose 30 connected to the concrete pump truck is connected to the pouring port 22 of the formwork 20.
Concrete is placed through 0.

An example of the mix of concrete used here is:
Concrete is made with ordinary aggregates, cement, etc., as well as an expanding agent made of delayed-reaction aluminum powder to ensure an appropriate amount of expansion (about 6% free expansion). 1-2 kg of reducing agent
It is desirable to add about 50 to 70 cm of slump flow to ensure the fluidity of the concrete.

Note that the above-mentioned expansion agent 1 separation reducing agent is added afterward at the concrete placement site.

Then, as concrete pouring progresses and concrete flows from the discharge port 24 located at the same level as the concrete pouring port 22, the opening/closing valve 26 of the discharge port 24 is opened.
Close.

Thereafter, the portion reaching the lower surface of the basement floor slab 10 is press-fitted using a pump.

At this time, concrete flows out from the small interval 28,
Since these openings are small, they will be blocked by the aggregate in the concrete, so if sufficient pressure is applied to the poured concrete, the pressure of the concrete will increase within the formwork 20, and the concrete will be sufficiently filled within the formwork 20. After confirming that the concrete has been completely spread, the press-fitting of concrete is stopped and the on-off valve 26 of the pouring port 22 is closed.

After this, the poured concrete will be cured in this state until it hardens.

In such a curing state, the separation reducing agent suppresses the generation of breathing water in the concrete, and since the small gap 28 at the upper end of the formwork 20 is filled with aggregate etc., a slight pressure is applied from this area. Even if the concrete escapes to the outside, the inside of the formwork 20 is maintained in a pressurized state in which the concrete press-in pressure is slightly reduced due to the action of the expanding agent in the concrete.

After the poured concrete has hardened, the formwork 2
0 is removed, a partition wall 14 will be constructed between the slabs 10° and 12.

Now, if the partition wall 14 is constructed using the method described above, the concrete will be press-fitted into the formwork 20, so depending on the pressure of the concrete and the self-leveling property of the concrete due to the separation reducing agent, it is possible to use a vibrator or the like. In addition, since the inside of the formwork 20 is kept under pressure during the curing period of the concrete after pouring, the lower surface of the existing concrete structure is not a flat surface. However, a strong unity can be achieved.

In addition, although the partition wall 14 was illustrated as a new concrete structure in the said Example, implementation of this invention is not limited to this, For example, a pillar member etc. may be sufficient.

Further, it is not necessary to provide the discharge port 24 in the formwork 20, and the small interval 28 may be used as a discharge port for poured concrete.

(Effects of the Invention) As explained above in the embodiments, according to the method for placing new concrete that is jointly formed on the lower surface of an existing concrete structure according to the present invention, the expanded concrete that is press-fitted into the formwork is The concrete containing the agent and separation reducing agent is then maintained under pressure for a predetermined period of time, and the generation of breathing water is suppressed, making it possible to firmly integrate the joint surface between the existing concrete and the new concrete. .

In addition, by press-fitting the poured concrete, the concrete is sufficiently distributed in the narrow space, eliminating the need for compaction using vibrators, etc., and also eliminating the need for filling the joint surface with epoxy resin, etc. Therefore, it is possible to significantly shorten the construction period.

[Brief explanation of the drawing]

Figures 1 to 3 show an embodiment of the method of this invention, with Figure 1 being an explanatory diagram of the construction state, Figure 2 being a sectional view of the main part of Figure 1, and Figure 3 being the completed construction. An explanatory diagram of the state, FIG. 4 is an explanatory diagram of construction using the conventional method. 10・・・・・・・・・・・・Basement-floor slab (existing concrete structure) 12・・・・・・・・・・・・Second-basement floor slab 14・・
・・・・・・・・・・Bulkhead (new concrete structure)
20・・・・・・・・・・・・Formwork 22・・・・・・・・・Casting port 26・・・・・・・・・・・・Opening/closing valve 28...・・・・・・・・・Small interval patent applicant Representative Obayashi Co., Ltd.
Person Patent Attorney - Kensuke Shiro Same Masatoshi Matsumoto Figure 1] 2 Figure 2 Figure 3 n Figure 4 (a) (b) (c) (d)

Claims (1)

[Claims] (1) In a method for placing new concrete that is jointly formed on the lower surface of an existing concrete structure, a concrete pouring opening that can be opened and closed is provided in the formwork for the new concrete, and the upper end of the formwork is Concrete is placed at a small distance from the bottom surface of the existing concrete structure, and concrete containing a separation reducing agent and an expansion agent is pressed into the formwork through the pouring port until it reaches the bottom surface of the existing concrete structure. A method for pouring new concrete in which a joint is formed on the lower surface of an existing concrete structure, the method comprising: and then closing a concrete pouring opening.