JP2001040659A - Concrete placing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely control cracking of mass concrete due to a temperature at a low cost. SOLUTION: A concrete of low heating type relatively lower than a concrete to be placed in a preceding section is used as a concrete to be placed in a subsequent section when the concrete is to be placed by dividing into the preceding section and the subsequent section in construction work for a concrete structure. A portland cement or Portland blast furnace slag cement is used normally as a concrete to be placed in the preceding section, and low heating type cement such as low-heat Portland cement is used as a concrete to be placed in the subsequent section. When a diaphragm wall 3 using a lower section as a cutoff wall 1 and an upper section as an earth retaining wall 2 is to be constructed, concrete of heating type relatively lower than the concrete of the cutoff wall of the subsequent section and the whole preceding section is employed as a concrete to be placed in the earth retaining wall of the subsequent section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concrete casting method applied when constructing a large-scale concrete structure such as a continuous underground wall.

[0002]

2. Description of the Related Art When constructing a large-scale concrete structure such as a dam or a continuous underground wall, it is naturally impossible to cast concrete on the entire structure at once. It is inevitable that the installation areas should be properly divided and sequentially installed. For example, when constructing a continuous underground wall, a leading part (leading element) and a trailing part (later element) are set, and concrete is poured into the leading part for a predetermined period (usually about 30 days). After the elapse), concrete is poured into the succeeding part in a form that is connected to the leading part.

Incidentally, as is well known, concrete generates heat due to a hydration reaction in the course of hardening, and especially in the case of mass concrete, the internal temperature may rise to about 80 ° C., and therefore, during the hardening process. Significant thermal expansion and subsequent contraction occurs. And, when concrete is poured into the leading portion and the trailing portion as described above, the thermal expansion and contraction of the trailing portion of the concrete are restrained by the leading portion concrete, so that a temperature crack occurs. May need to be addressed.

Conventionally, as a measure for controlling the temperature cracking of mass concrete as described above, a pre-cooling method for cooling fresh concrete using a low heat type concrete using a low heat type cement to suppress heat generation of the concrete itself. And forced cooling by charging a water circulation pipe into cast concrete.

[0005]

However, all of the above measures require a great deal of cost and have not been widely used. In particular, concrete of low heat generation type is considerably expensive compared to ordinary concrete, so it is not practical to use it for all of the huge amount of concrete in terms of cost, and also in terms of crack control effect. It is not always sufficient, and therefore, an effective measure that can control the temperature cracking of the mass concrete inexpensively and reliably has been desired.

[0006]

Although the present invention uses low heat-generating concrete, the present invention does not use all of the concrete as low heat-type concrete as in the prior art, but uses the concrete only in important places. Therefore, it is possible to realize a significant cost reduction as compared with the case where the entire concrete is made of a low heat generation type concrete, and also it is possible to enhance a crack control effect.

That is, according to the first aspect of the present invention, when constructing a concrete structure, the area where the concrete is to be cast is divided into a leading part and a trailing part which are adjacent to each other, and the concrete is poured into the leading part. In the concrete casting method in which concrete is poured into the succeeding part after the elapse of a predetermined period after the installation, the concrete to be poured into the trailing part has a lower heat generation type than the concrete poured into the preceding part. Of concrete.

According to a second aspect of the present invention, there is provided the concrete casting method according to the first aspect of the present invention, wherein ordinary portland cement or blast furnace cement is used as the cement in the concrete to be cast in the leading portion, and the concrete to be cast in the succeeding portion. A low heat type cement such as a low heat Portland cement is used as the cement.

According to a third aspect of the present invention, when constructing a continuous underground wall having a lower portion as a water blocking wall and an upper portion as a retaining wall, the continuous underground wall is divided into a leading portion and a trailing portion which are adjacent to each other. In the concrete casting method in which concrete is poured into the succeeding part after a predetermined period has elapsed after the concrete is poured into the preceding part, the concrete to be poured into the retaining wall of the trailing part is used as the concrete. Concrete that generates relatively less heat than the water blocking wall in the row section and the concrete in the entire preceding section is used.

According to a fourth aspect of the present invention, there is provided the concrete casting method according to the third aspect of the present invention, wherein ordinary portland cement or blast furnace cement is used as the cement in the concrete to be cast on the waterproof wall of the entire preceding portion and the following portion. A low heat type cement such as a low heat Portland cement is used as the concrete in the concrete to be cast on the retaining wall of the trailing part.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to the construction of a continuous underground wall will be described below. In the present embodiment, concrete is cast on the leading portion in the same manner as before, and then concrete is placed on the trailing portion after a lapse of a predetermined period, but different types of cement are used in the leading portion and the trailing portion. As the concrete, the concrete of the lower heat generation type is used as the concrete of the succeeding part (the succeeding concrete) as the concrete of the succeeding part (preceding concrete). Concretely, low-heat type concrete using low-heat type cement such as low-heat Portland cement as low-heat portland cement is used as the subsequent concrete using low-heat portland cement or normal concrete using blast furnace cement type B as the cement used for the preceding concrete. .

FIG. 1 shows a temperature change state after placing the preceding concrete and the following concrete. Is the precedent concrete made of ordinary concrete.
After the temperature rises to about 80 ° C. per day, the temperature gradually decreases and finally reaches room temperature. Is a post-concrete made of low heat type concrete cast about 30 days later than the preceding concrete, and reaches a maximum temperature about 5 days after casting, but the temperature remains at about 60 ° C. Then, a maximum temperature difference ΔT1 occurs between the preceding concrete and the subsequent concrete when the subsequent concrete reaches the maximum temperature.

It goes without saying that the maximum temperature difference ΔT1 is greatly reduced as compared with the case where ordinary concrete is used for both the leading concrete and the succeeding concrete as in the prior art. As described above, the present invention can be improved as compared with the case where low-heating type concrete is used for both the leading concrete and the succeeding concrete.

This will be further described with reference to FIG. In the figure, the broken line shows the temperature change situation when the same low-heating type concrete as the subsequent concrete is used as the preceding concrete. In this case, the temperature change of the preceding concrete is the same as the temperature change of the subsequent concrete, so the maximum temperature is lower than that of ordinary concrete, but the subsequent concrete which affects the temperature crack of the subsequent concrete And the maximum temperature difference ΔT2 increases. In other words, when the same low-heating type concrete as the succeeding concrete is used as the preceding concrete, the temperature difference from the succeeding concrete is reduced by ΔT due to the suppression of the temperature rise as compared with the case of using the ordinary concrete. However, it is disadvantageous from the viewpoint of temperature crack control.

2 to 4 show detailed comparison data. 2 shows the temperature change state of the concrete as in FIG. 1, FIG. 3 shows the internal stress of the concrete, FIG. 4 shows the crack index, and (a) shows the practice of the present invention. This is a form (normal concrete is used as the preceding concrete, and low heat-generating concrete is used as the succeeding concrete), and (b) is a conventional method (both use low heat-generating concrete).

From FIG. 2, it is clear that, as already shown in FIG. 1, the maximum temperature difference between the preceding concrete and the following concrete is improved in this embodiment as compared with the conventional method. Further, from FIG. 3, the internal stress finally becomes the tensile side (positive side) in the conventional method, whereas the internal stress stays on the compression side (minus side) in the present embodiment, so that cracks are unlikely to occur. I understand.

Further, from FIG. 4, it can be seen that the crack index is maintained at about 1.2 or more in the present embodiment, but remains at 0.7 in the conventional method. The crack index (I) is a value obtained by dividing the tensile strength (f) of the concrete by the temperature stress (σ: increased stress from the maximum value of the compressive stress; see FIG. 3). It can be determined that it has crack control performance. FIG.
The crack index shown in (1) is obtained by calculating the tensile strength of each material age by experiment and calculating the temperature stress by heat conduction analysis and temperature stress analysis by FEM, and calculating from these values.

According to the above method, by using ordinary concrete as the leading concrete and using low-heating type concrete only for the succeeding concrete, the cost can be reduced as compared with the case where all of the concrete is made of low-heating type concrete. In addition to the above, there is an effect that temperature cracks can be more effectively controlled.

The longer the period from the placement of the preceding concrete to the placement of the subsequent concrete, the greater the maximum temperature difference between them, the more the subsequent concrete becomes possible from the viewpoint of crack control. It is preferable that the casting be performed quickly.

In the above embodiment, the entire subsequent concrete is made of the low heat-generating concrete. However, the concrete is further divided and the low heat-generating concrete is used only for a part of the subsequent concrete, and the others are made of ordinary concrete. It is also possible. For example, in recent years, as shown in FIG. 5, there is a case where a continuous underground wall 3 in which a lower part is a water blocking wall 1 and an upper part is a retaining wall 2 is constructed, and such a continuous underground wall 3 is constructed. In doing so, use ordinary concrete for the entire leading section (water blocking wall 1 and retaining wall 2) and the trailing water blocking wall 1, and use only low heat generation concrete for the trailing retaining wall 2 only. Can be considered. In this case, the temperature crack control performance of the water blocking wall 1 in the trailing portion is slightly lowered, but the temperature crack of the retaining wall 2 can be sufficiently controlled, and the cost can be further reduced.

Further, in the above embodiment, the present invention is applied to the construction of the continuous underground wall. However, the present invention is not limited to the continuous underground wall, but is generally applied to the construction of a concrete structure in which the temperature crack is a problem. Naturally, it can be widely applied to
It is needless to say that the ordinary concrete and the low heat generation type concrete are not limited to those exemplified above, and any concrete having similar properties can be used.

[0022]

According to the first aspect of the present invention, since concrete having a relatively low heat generation is used as the concrete to be cast into the trailing portion, concrete having a relatively low heat generation is used as the concrete to be cast into the preceding portion. In addition to the cost reduction, it is possible to more effectively control temperature cracks.

The invention of claim 2 uses a low-heat-type cement such as low-heat Portland cement as cement in concrete to be cast in the leading part, using ordinary Portland cement or blast furnace cement as concrete in the latter. Since it is used, in each case, a commercially available concrete product can be used as it is, and an excellent temperature crack control effect can be obtained.

According to a third aspect of the present invention, when constructing a continuous underground wall having a lower portion as a water blocking wall and an upper portion as a retaining wall, the concrete to be cast on the following retaining portion is used as the entirety of the preceding portion. And, since concrete of relatively low heat generation is used than concrete cast on the water stop wall of the trailing part, it is possible to control the temperature cracking of the retaining wall of the trailing part and to reduce the cost. You can also.

According to a fourth aspect of the present invention, there is provided a concrete which is cast on the retaining wall of the trailing part by using ordinary Portland cement or blast furnace cement as the cement in the concrete to be placed on the water stopping wall of the entire leading part and the trailing part. Since a low heat-generating cement such as low heat Portland cement is used as the cement in the above, an excellent temperature crack control effect can be obtained by using a commercially available concrete product as it is.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temperature change state of concrete poured by the method of the present invention.

FIG. 2 is a diagram showing a concrete temperature change state of the method of the present invention and the conventional method.

FIG. 3 is a diagram showing concrete stresses of the method of the present invention and a conventional method.

FIG. 4 is a diagram showing concrete crack index of the method of the present invention and the conventional method.

FIG. 5 is a diagram showing a configuration example of a continuous underground wall to which the present invention is applied.

[Explanation of symbols]

 1 water stop wall 2 mountain retaining wall 3 continuous underground wall

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Katsuhiko Kimura Inventor F-term (reference) 2D049 EA01 EA02 GB02 GC00 1-3-2 Shibaura, Minato-ku, Tokyo

Claims (4)

[Claims] When constructing a concrete structure,
The area where concrete is to be cast is divided into a leading part and a trailing part which are adjacent to each other, and after the concrete is placed on the leading part, concrete is placed on the trailing part after a predetermined period has elapsed. In the casting method, a concrete with lower heat generation is used as the concrete to be placed in the trailing part than the concrete to be placed in the preceding part. 2. The concrete casting method according to claim 1, wherein ordinary Portland cement or blast furnace cement is used as the cement in the concrete to be cast in the leading portion, and low-heat Portland cement or the like as the cement in the concrete to be cast in the succeeding portion. Concrete casting method characterized by using the low heat generation type cement. 3. When constructing a continuous underground wall having a lower part as a water blocking wall and an upper part as a retaining wall, the continuous underground wall is divided into a leading part and a trailing part which are adjacent to each other, and the leading part is formed as a leading part. After the concrete is cast, the concrete is poured into the trailing part after the elapse of a predetermined period, and the concrete is poured into the retaining wall of the trailing part. A concrete casting method, wherein concrete having a lower heat generation is used than concrete of the entire wall and the leading portion. 4. The concrete casting method according to claim 3, wherein ordinary portland cement or blast-furnace cement is used as the cement in the concrete to be cast on the water blocking wall of the entire leading portion and the trailing portion, and the retaining portion of the trailing portion is provided. A concrete casting method characterized by using low heat type cement such as low heat Portland cement as cement in concrete to be cast on a wall.