JPH10280687A - Concrete placement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To construct a mass concrete structure of the required strength at high workability by applying the constitution that high fluidity concrete having the prescribed slump flow range is placed in the placement space of existing concrete in advance, and curing the high fluidity concrete after supplying coarse aggregate thereto. SOLUTION: First, placement space 2 using existing concrete 1 as a bottom part is formed, and the side of the space 2 is made by use of a form. At the process of the prior placement of high fluidity concrete, preferably lime stone powder or the like is used to substitute a part of cement and high fluidity concrete 3 blended with a thickener and prepared to have a slump flow between 60 and 80 cm is placed in the space 2. Thereafter but before the lapse of long time, coarse aggregate 4 is supplied to the high fluidity concrete 3 from an upper position. As a result, the level of the placed concrete rises and in this case, placement height after the supply of the coarse aggregate 4 is preferably set at a level approximately between 50 and 100 cm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing a mass concrete structure such as a concrete dam or an anchorage with good workability.

[0002]

2. Description of the Related Art Conventionally, mass concrete structures such as concrete dams are generally constructed using hardened concrete or ultrahardened concrete. The use of such hardened concrete for dam construction is mainly due to the following reasons.

(1) In mass concrete such as a dam, there is a problem of temperature cracking due to heat of hydration of cement. As a result of reducing the amount of cement to minimize the heat of hydration, the required strength is reduced. In order to obtain it, the unit water volume is inevitably reduced, which leads to stiffening. (2) In the case of mass concrete structures such as dams, the casting surface is wide, but if the concrete is soft, it sinks into the concrete poured by the machine or human when the machinery is moved or compacted. Therefore, the workability becomes extremely poor.

[0004] Therefore, various rational construction methods and equipment have been proposed and developed on the premise of using such hardened concrete, and many of them have been put to practical use (for example, RCD method, ELCM, etc.). .

[0005]

The most difficult item to be rationalized in concrete construction is the compaction of concrete. However, compaction of hardened concrete is extremely difficult. There is a problem that cannot be rationalized. In recent years, compaction by a machine such as buy back (vibro reach) has been performed, but it does not reach every corner and there are not many parts compacted by hand. Although the RCD method uses rollers for compaction, considerable rationalization has been achieved, but there are still limitations.

An object of the present invention is to solve the above problems and to construct a mass concrete structure having required strength with good workability.

[0005]

According to the present invention, in the construction of a mass concrete structure in which concrete is sequentially transferred from a lower part to an upper part, a casting space is formed on existing concrete, and the casting space is formed. The slump flow is 55-
Provided is a concrete construction method characterized by pre-punching 80 cm of high-fluidity concrete, post-injecting coarse aggregate into the pre-punched high-fluidity concrete, and hardening.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a new mass concrete construction method which fundamentally changes the conventional method using hardened concrete and solves the problems of temperature stress and workability at once. First, after the high-fluidity concrete is hit first, coarse aggregate of the designed blending amount is injected into the high-fluidity concrete from above.

[0007]

1 and 2 show an embodiment of the present invention. A casting space 2 is formed on an existing concrete 1 and, first, as shown in FIG. 2 shows a state in which high-fluidity concrete 3 is poured into the concrete 2 and then coarse aggregate 4 is put in from above the high-flowable concrete 3 that has been poured in as shown in FIG.

According to the method of the present invention, a casting space 2 having an existing concrete 1 as a bottom is first formed, and its side is formed by using a form 5. In the example shown in the figure, the side wall forming the casting space 2 is formed by using the formwork 5, but one or three sides of the side of the casting space 2 may be existing concrete. That is, when a hardened concrete body that has already been cast has been formed on the side, the side surface of the hardened concrete body can be replaced with a formwork of the space to be cast.

The mold 5 can be a buried mold. That is, the formwork 5 may be buried as it is after the temporary mission is completed, and in this case, a precast concrete one is suitably used. Also RC
(Reinforced concrete) Formwork and the like can be used as appropriate. A broken line 6 shown in the existing concrete 1 in the figure indicates a buried form.

In this manner, the casting space 2 is formed by using the existing concrete as the bottom (and part of the side), and as shown in FIG. I do. This pre-cast high fluidity concrete 3 has a slump flow of 55 to 80 cm, preferably 6 to 80 cm.
Those having high fluidity of 0 to 80 cm, more preferably 65 to 75 cm are used.

Originally, high-fluidity concrete can be cast into every corner without material separation in reinforcing bars or narrow spaces without compaction work such as a vibrator or the like, and bleeding and latency are small. It was developed in order to obtain such a property, and in this sense, the main purpose was to have excellent self-filling properties. For example, Japanese Patent Application Laid-Open No. 3-455
No. 44, JP-A-5-279101, etc., a material separation reducing agent (thickening agent), a high-performance water reducing agent, an AE agent, etc. are appropriately compounded and the amount of powder is increased. It has a slump flow of 50 to 75 cm and an air volume of 3 to 5%, and has the property of naturally flowing into gaps by its own weight.

[0012] The method of the present invention is based on the idea that the excellent self-filling property of such high-fluidity concrete is utilized for the filling and filling property of the later-charged coarse aggregate. The fluid concrete and the post-input coarse aggregate are integrated, enabling the construction of a strong mass concrete structure. For this reason, the high fluidity concrete used in the method of the present invention using welan gum as a thickener is suitable for the method of the present invention.

Welan gum has a cell number of Alcaligenes ATC
It is a microbial fermented polysaccharide produced by C 31555 species and can increase the material separation resistance without sacrificing the fluidity of highly fluid concrete. As the high-performance water reducing agent, a commonly used polycarboxylate, β-naphthalenesulfonate, melaminesulfonate and the like can be used, and a commonly used AE agent can also be used.

High fluidity concrete has a large amount of powder, usually about 500 kg / m ³ . Therefore, if this powder is all cement, the temperature rise characteristics will be quite high (for example, at an implantation temperature of 20 ° C. and a moderate heat Portland cement of 500 kg / m ³ , the adiabatic temperature rise amount will be 60 to 65 ° C.). ), If the total volume ratio of the coarse aggregate already mixed in the high-fluidity concrete and the coarse aggregate to be charged later is, for example, 60%, the cement amount becomes about 200 kg / m ^{3 in} the total unit volume, It is the same level as cement amount of hardened concrete of general concrete dam. Therefore, even when all of the powder of the high-fluidity concrete is cement, the temperature rise is equivalent to that of the conventional hardened concrete. However, the compressive strength of the high-fluidity concrete part existing between the coarse aggregates is 40 N / mm.
Considering that a mass concrete structure such as a dam can be constructed even if it is about ^2, about 40% of the powder can be replaced with powder other than cement, such as limestone powder.
Due to this reduction in the amount of cement, it is very advantageous against temperature stress as compared with conventional hardened concrete.

As for the aggregate to be mixed with the high-fluidity concrete, in addition to ordinary fine aggregate, coarse aggregate having a maximum dimension of about 20 mm or less, preferably 15 mm or less is mixed. As a result, the coarse aggregate is cast into the gaps between the large coarse aggregates that have been introduced later, and the coarse aggregates can be firmly joined without compaction. Also, the one without bleeding or latency is used. This eliminates the need for a green cut on the casting surface. Also, as the aggregate, only fine aggregate can be used, and a soft mortar in which coarse aggregate is not mixed can be pre-punched by the method of the present invention. In this case as well, it is necessary that the mortar has a fluidity such that the coarse aggregate to be charged later is naturally filled uniformly under its own weight in the vertical mortar layer. It is preferable to appropriately mix in an admixture for the above. As the admixture, those similar to those used for high-fluidity concrete can be used.

Thus, in the pre-stage of the high-fluidity concrete shown in FIG. 1, most preferably, a part of the cement is replaced with limestone powder or the like and welan gum as a thickener is blended with a slump flow of 60 to 80 cm. The high fluidity concrete 3 is cast in the casting space 2. This casting operation can be performed using a pump, and the casting thickness is 20 to 60 c.
m, preferably 25 to 50 cm, more preferably 25 to 50 cm
40 cm.

When the casting of the high-fluidity concrete 3 is completed, the coarse aggregate 4 is poured into the high-fluidity concrete 3 from above without leaving much time, as shown in FIG. The post-coarse coarse aggregate may have a size of 5 to 100 cm, and the total mass of pre-poured high-fluid concrete or mortar and post-coarse coarse aggregate is to be the target mass concrete composition. Determine the amount of coarse aggregate to be charged later. The coarse aggregate can be transported by using a dump or a bucket or a vessel in the case where a crane is used, in addition to directly transporting the coarse aggregate to a setting position. Particularly, in the case of a vessel, it is convenient to use a vessel with an open bottom, since the vessel can be conveyed directly above the casting space 2 and loaded as it is.

The cast concrete surface rises due to the post-injection of the coarse aggregate 4, but the casting height after the completion of the introduction of the coarse aggregate 4 is 40 to 150 cm, preferably 50 to 100 cm.
It is good to set to about cm. If the height is too shallow, the work efficiency will be low, and if it is too deep, the distribution of coarse aggregate to be charged later may not be uniform.

When the coarse aggregate 4 is charged,
A method in which particles having different particle diameters are mixed so as to have an appropriate particle size distribution and then charged, a method in which a particle having a large particle diameter is charged first, and a method in which a particle having a small particle diameter is charged later, and a method in which a powder is injected are used. When the area of the installation space 2 is relatively large, the coarse aggregate 3 is first submerged in the lower layer portion of the layer of the high fluidity concrete 3 while moving the vessel 7 and the like so as to have a uniform thickness. A method of pouring the remaining coarse aggregate 3 into the upper high-fluid concrete layer while leveling the coarse aggregate 3 or the like can be appropriately adopted according to the site.

It is desirable to use a pre-cooled coarse aggregate 4 in order to minimize temperature stress, especially in summer. Various methods of pre-cooling the aggregate are known, and a method using a freezer, a method using liquid nitrogen, a watering method, and the like can be applied. Further, the temperature stress can be adjusted by adjusting the mixing ratio of the coarse aggregate to be mixed into the high-fluidity concrete and the later-input coarse aggregate.

When a predetermined amount of the coarse aggregate 4 has been charged in this way, a curing reaction can be performed as it is. That is, compaction is not required except in special cases. Then, on this hardened concrete layer, and possibly on the semi-hardened concrete layer,
The operation of pre-casting high-fluidity concrete and then post-feeding coarse aggregate is repeated. In this case, the height of the initial casting space 2 is sufficiently set, and within one casting space 2,
The method of the present invention can be sequentially carried out and spliced upward, or in one casting space 2, the method of the present invention can be carried out only once.
On top of that, if necessary, a new casting space 2
Can be formed and joined. In either case,
As described above, it is convenient to use a buried mold, but in some cases, it is of course possible to remove the mold and reuse it. At that time, a construction method such as a layer method in which only a horizontal seam is provided in a mass concrete structure or a block method in which a crack for post-filling is provided can be appropriately employed.

The mass concrete structure completed by carrying out the method of the present invention is a structure in which coarse aggregates are firmly connected to each other by hardened cement without compaction, and coarse bones to be injected later. By using cold material, the problem of temperature cracking can be solved.

[0023]

As described above, the method of the present invention is applicable to mass concrete construction such as dams and anchorages.
Compared with the conventional method using hardened concrete, it has an excellent effect that the workability is improved while solving the problem of the temperature crack while being comparable in strength.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a construction example showing a pre-stage of high-fluidity concrete according to the method of the present invention.

FIG. 2 is a schematic cross-sectional view of a construction example showing a coarse aggregate input stage according to the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Existing concrete 2 Casting space 3 High fluidity concrete 4 Post-input coarse aggregate 5 Formwork 6 Buried formwork 7 Coarse aggregate input vessel

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Ouchi Kashima Construction Co., Ltd. 3-3-1 Bandai, Niigata City, Niigata Prefecture

Claims (5)

[Claims] In a construction of a mass concrete structure in which concrete is sequentially transferred from a lower part to an upper part, a casting space is formed on the existing concrete, and a slump flow of 55 to 80 cm is formed in the casting space. A concrete construction method characterized by pre-casting concrete and post-injecting coarse aggregate into the pre-cast high-fluid concrete to harden. 2. The concrete construction method according to claim 1, wherein a soft mortar is used in place of the high fluidity concrete. 3. The method according to claim 1, wherein the high-fluidity concrete contains welan gum as a thickener. 4. The concrete construction method according to claim 1, wherein the coarse aggregate to be charged later is pre-cooled. 5. The concrete construction method according to claim 1, wherein the casting space is formed using a buried mold.