JP3013351B2 - How to prevent mass cracking of mass concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing thermal cracks in mass concrete, and more particularly to a method for preventing thermal cracks in mass concrete at the beginning of casting.

[0002]

2. Description of the Related Art In the case of a concrete structure having a large member cross section, the heat of hydration of the cement is accumulated near its center and the internal temperature rises. Become uneven,
So-called temperature cracks tend to occur. When such a temperature crack occurs, it is necessary to handle it as so-called mass concrete in design or construction.

[0003] As a method of preventing temperature cracks in mass concrete, the maximum temperature of the concrete and the temperature gradient in the cross section are made as small as possible by artificial cooling such as pipe cooling or pre-cooling, or by using low heat generating concrete. There are known ways to do this.

[0004]

However, in the method using artificial cooling, particularly pipe cooling, piping is troublesome, and low heat-generating concrete has a high unit price, and in any case, the cost of concrete construction is high. Was.

The present invention has been made in consideration of the above circumstances, and has as its object to provide a method of preventing mass cracking of mass concrete at low cost.

[0006]

In order to achieve the above object, a method for preventing cracking of mass concrete according to the present invention is characterized in that, in a predetermined casting region for forming mass concrete, a center portion is formed. The concrete that is poured into the part has a lower heat generation rate than the concrete that is poured into the peripheral part.

According to the method for preventing temperature cracking of mass concrete according to the present invention, the concrete poured into the peripheral portion is made by using ordinary Portland cement, and the concrete poured into the central portion is made of medium heat Portland cement or It is manufactured using low heat generating cement.

[0008]

According to a third aspect of the present invention, there is provided a method for preventing temperature cracking of mass concrete, wherein concrete poured into a lower layer is replaced with concrete poured into an upper layer in a predetermined casting area for forming mass concrete. Also, concrete with a low heat generation rate, a low heat generation rate, or a low driving temperature is used.

[0010]

In the method for preventing mass cracking of mass concrete according to the present invention, the concrete poured into the central portion is a concrete having a lower heat generation rate than the concrete poured into the peripheral portion. Then, the heat of hydration hardly accumulates in the central portion, the temperature distribution of the entire cross section becomes nearly uniform, and the temperature crack is reduced.

[0011]

Further, in the method for preventing cracking of mass concrete according to the present invention, the concrete to be poured into the lower layer is a concrete having a lower heating value or a lower heating rate than the concrete to be poured into the upper layer, or a concrete to be poured at a lower temperature. Then, heat of hydration hardly accumulates in the lower layer, and the temperature distribution of the entire cross section becomes nearly uniform, thereby reducing temperature cracking.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for preventing thermal cracking of mass concrete according to the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) In the method for preventing thermal cracking of mass concrete according to the present embodiment, concrete is produced by mixing ordinary Portland cement and low heat-generating cement in a state where the total cement amount is substantially constant. Then, this is divided into several layers and cast into a casting area 1 shown in FIG. 1 (a) to form a mass concrete. Here, in the central portion, that is, in the intermediate layer 2, the ratio of the low heat-generating cement having a small heat generation amount and heat generation rate is increased, and the ratio of the low heat-generating cement is reduced as it is closer to the peripheral portion, that is, the lowermost layer 3 and the uppermost layer 4.

FIG. 1 (b) is a schematic diagram showing the mixing ratio of ordinary Portland cement and low heat-generating cement. As can be seen from the figure, near the bottom layer, ordinary Portland cement and low heat-generating cement are mixed appropriately and injected, but as it moves upward, the proportion of ordinary Portland cement is gradually reduced, and the intermediate layer mainly has low heat generation. Driving concrete made of cement.

On the other hand, from the intermediate layer to the uppermost layer, the cement is poured while increasing the proportion of ordinary Portland cement, and concrete made mainly of ordinary Portland cement is used for the uppermost layer.

As described above, when the low heat-generating cement is mainly used in the intermediate layer, and the proportion of the ordinary Portland cement is increased nearer the uppermost layer and the lowermost layer, the calorific value and the heat generation rate in the intermediate layer are as follows. Therefore, the heat value and the heat generation rate in the uppermost layer or the lowermost layer are smaller than those in the uppermost layer or the lowermost layer, and the heat of hydration hardly accumulates inside. As a result, as shown in FIG. 2 (a), the temperature distribution in the cross section becomes more uniform as compared with the case where only ordinary cement is used (indicated by the broken line), and the stress distribution is correspondingly shown in FIG. As shown in Fig. 2 (b), the size is smaller than when only ordinary cement is used.

As described above, according to this embodiment,
The mixing ratio of low heat-generating cement was increased in the middle layer, and decreased near the bottom and top layers.This minimized the use of expensive low heat-generating cement while minimizing temperature cracks in mass concrete. It becomes possible to suppress efficiently.

In this embodiment, concrete having a small calorific value and a small heat generation rate is produced by using a low heat-generating cement, but it may be produced by using a medium heat cement instead. Further, the amount of heat and the rate of heat generation may be reduced by reducing the amount of unit cement.

Further, in this embodiment, the mixing ratio of the ordinary cement and the low heat-generating cement is changed continuously in the height direction, but may be changed discontinuously, that is, stepwise.

(Second Embodiment) Next, a second embodiment will be described. Also in the present embodiment, mass concrete is formed by dividing predetermined concrete into several layers in the casting area 1 shown in FIG. 1 (a). Then, the implantation temperature is set higher near the periphery, that is, the lowermost layer 3 and the uppermost layer 4.

FIG. 3 shows an example of setting the concrete driving temperature. In adjusting the driving temperature, concrete of normal temperature is used for the lowermost layer 3 and the uppermost layer 4 and concrete cooled in advance is used for the intermediate layer 2 by appropriately considering the outside air temperature and the like. Alternatively, conversely, preheated concrete may be used for the lowermost layer 3 and the uppermost layer 4, and ordinary concrete may be used for the intermediate layer 2.

In this manner, the difference in temperature of the concrete at the time of casting cancels out the effect of increasing the temperature in the central part due to the heat of hydration, and as a result, the temperature distribution and the stress distribution in the cross section as described with reference to FIG. Becomes more uniform and temperature cracks are reduced.

As described above, according to the present embodiment,
Since the temperature of concrete poured into the center is lower than the temperature of concrete poured into the periphery, it is possible to make the temperature distribution in the cross section nearly uniform at low cost and efficiently suppress temperature cracks. It becomes possible.

(Third Embodiment) Next, a third embodiment will be described. In this embodiment, the casting area 1 shown in FIG. 4 is divided into an upper layer 11 and a lower layer 12, and concrete made of low heat-generating cement is poured into the lower layer 12, and
1 Place concrete made of ordinary cement.

As described above, when the lower layer 12 is made of a low heat-generating cement and the upper layer 11 is made of ordinary Portland cement, the calorific value and the heating rate of the lower layer are smaller than the calorific value and the heating rate of the upper layer. And the heat of hydration is less likely to accumulate in the lower layers. As a result, the temperature distribution in the cross section becomes almost uniform as described with reference to FIG.

Therefore, also in this embodiment, while minimizing the amount of costly low-heat-generating cement used,
It is possible to efficiently suppress the temperature crack of the mass concrete. In this embodiment, moderate heat cement may be used in place of the low heat-generating cement, or the calorific value and the heat generation rate may be reduced by reducing the unit cement amount.

Alternatively, the temperature of the concrete poured into the lower layer 12 may be lowered and the temperature of the concrete poured into the upper layer 11 may be increased.

In this case, the temperature difference of the concrete at the time of casting is offset by the effect of raising the temperature of the lower layer due to the heat of hydration. It becomes more uniform and temperature cracks are reduced.

[0030]

As described above, according to the method for preventing mass cracking of mass concrete according to the first aspect of the present invention, temperature cracking of mass concrete can be reduced at low cost.

[0031]

Further, according to the method for preventing temperature cracks of mass concrete according to the third aspect of the present invention, the temperature cracks of mass concrete can be reduced at low cost.

[0033]

[Brief description of the drawings]

FIG. 1 (a) is a view showing a state in which mass concrete is formed using the method for preventing temperature cracking of mass concrete according to the first embodiment, and (b) is a mixing ratio of ordinary cement and low heat-generating cement. FIG.

FIG. 2 is a diagram showing a change in temperature distribution and a change in stress distribution in a cross section when mass concrete is formed according to the method of the present embodiment.

FIG. 3 (a) is a diagram showing a state in which mass concrete is formed by using the method for preventing temperature cracking of mass concrete according to the second embodiment, and FIG. 3 (b) is a setting example of a concrete setting temperature at that time. FIG.

FIG. 4 is a view showing a state in which mass concrete is formed by using the method for preventing temperature cracking of mass concrete according to the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casting area 2 Intermediate layer 3 Bottom layer 4 Top layer 11 Upper layer 12 Lower layer

Continuation of the front page (56) References JP-A-61-165458 (JP, A) JP-B-4-15346 (JP, B2) JP-B-61-32453 (JP, B2) (58) Fields investigated (Int) .Cl. ⁷ , DB name) E04G 21/02 104

Claims (3)

(57) [Claims] 1. A temperature-cracked mass concrete, wherein a concrete poured into a central portion of the predetermined casting region for forming the mass concrete has a lower heating rate than a concrete poured into a peripheral portion. Prevention method. 2. The mass according to claim 1, wherein the concrete poured into the peripheral portion is produced using ordinary Portland cement, and the concrete poured into the central portion is produced using medium heat Portland cement or low heat-generating cement. How to prevent temperature cracks in concrete. 3. In a predetermined casting area for forming mass concrete, the concrete poured into the lower layer is made concrete having a lower heating value, a lower heat generation rate or a lower casting temperature than the concrete poured into the upper layer. Characteristic method for preventing mass cracking of mass concrete.