JP3528902B2 - Preventing cracks in concrete structures - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preceding concrete structure and a succeeding concrete structure which are disposed adjacent to each other via a joint surface, such as an underground continuous wall. TECHNICAL FIELD The present invention relates to a method for preventing cracks in a concrete structure, which is applied to the construction of a concrete structure having a structure and prevents the occurrence of cracks inside the concrete structure. 2. Description of the Related Art In mass concrete structures, such as underground continuous walls and dams, in which concrete is cast as a large mass at one time, the internal temperature rises due to the accumulation of heat of hydration of cement. This tends to cause large tensile stress due to subsequent cooling, which may cause temperature cracking. Therefore, various methods for preventing such temperature cracks have been proposed. Among these methods, considering materials and compounding aspects, use cements with low heat of hydration such as blast furnace cement, fly ash cement, medium heat cement, and belite cement as cement materials. And a method of reducing the amount of unit cement as much as possible at the time of blending design to suppress the generation of heat of hydration in the concrete structure. Also, considering the construction side,
A method (pre-cooling) of lowering the temperature of concrete itself by cooling water or aggregate with liquid nitrogen when mixing concrete is used. [0004] However, even if only the material and the composition are adjusted as described above, when the thickness of the concrete is large,
At present, it is difficult to prevent temperature cracks when the temperature is high such as in summer or when high-strength concrete is used. In addition, the above-described method using pre-cooling has a problem that, although its effect is recognized, it lacks economy. In a mass concrete structure as described above, a concrete placement site is divided into a plurality of blocks, and construction is performed for each of these blocks sequentially to construct a concrete structure. Is often adopted. [0006] Therefore, there has been proposed a method of positively utilizing such a construction method to prevent cracks in a concrete structure. That is, when the concrete structure is constructed for each block as described above, pipes are provided in both the block formed earlier (the preceding block) and the block formed later (the succeeding block). In addition, these pipes are connected to each other to form a continuous pipe, and water is circulated through the pipe. [0007] In the method of constructing a concrete structure in which construction is performed sequentially for each block as described above, when the preceding block and the succeeding block are connected, heat of hydration of concrete is being accumulated in the succeeding block. In contrast, the preceding block has already been cooled to some extent. Therefore, by arranging the pipes and circulating the water as described above, the heat of hydration of the subsequent block is moved relative to the preceding block via the water circulating in the pipe, and the temperature of the subsequent block is reduced. Cracks can be prevented. Further, according to this method, it is possible to reduce the temperature difference at the joint surface, which occurs when the succeeding block is joined to the preceding block, at the boundary. Normally, when such a temperature difference is left, shrinkage deformation occurring in a portion of the succeeding block in the vicinity of the joint surface is restrained by the preceding block via the joint surface and becomes inside the succeeding block. Causes tensile stress, which may cause cracking. But,
According to the above-described method, an effect of reducing the temperature difference between the two can be obtained, so that an effect of preventing cracking due to the temperature difference between the preceding and succeeding blocks can be expected together. As an apparatus for performing such a method of transferring the heat of hydration of concrete from the succeeding block to the preceding block, for example, an apparatus shown in FIG. 4 filed by the present applicant is known. . A concrete structure crack preventing apparatus 1 shown in FIG. 4 is described in Japanese Patent Application Laid-Open No. Hei 7-217211, in which a preceding element (preceding concrete structure) 2 and a following element are arranged adjacent to each other. Cooling pipes 4 and 5 arranged inside each of the (following concrete structures) 3 and formed as continuous pipes, connecting pipes 7 connecting the cooling pipes 4 and 5 to each other, and a halfway of the connecting pipe 7 And a circulation pump 8 interposed therebetween. With the above-described structure, in the crack preventing device 1, water or the like is circulated through the cooling pipes 4, 5 and the connecting pipe 7, so that the leading and following elements 2,
3 can be reduced. [0012] However, the above-described crack preventing device 1 has room for improvement in the following points. First, when the above-described crack prevention device 1 is applied to an underground continuous wall, a dam or the like, the deformation of the preceding element 2 is often restricted from the periphery. As the temperature rises, stress will be generated inside the preceding element 2. Therefore, there is a concern that cracks may occur inside the preceding element 2. Further, in the above-described crack preventing device 1, in order to prevent the occurrence of cracks due to the temperature difference between the preceding and succeeding elements 2 and 3, the temperatures of the preceding and succeeding elements 2 and 3 are reduced. It was necessary to continue operation until it became almost constant. If the operation is terminated halfway, the hydration reaction of the concrete in the subsequent element 3 is in progress, while the hydration reaction of the concrete in the subsequent element 3 is in progress.
Is no longer supplied with heat, the temperature of the preceding element 2 drops, the temperature difference between the preceding and succeeding elements 2 and 3 increases, and the effect of preventing cracking is lost. However, when the crack prevention device 1 is operated as described above, the time required for the operation is long, and for example, when construction work is performed at a plurality of locations at the same site, the same operation is performed. It becomes difficult to use the device sequentially at a plurality of locations. As a result, connection pipe 7
And a large number of circulating pumps 8 must be prepared, which is economically expensive. The present invention has been made in view of such circumstances, and can prevent the generation of stress inside the preceding concrete structure, and can shorten the operation time as compared with the related art. It is an object of the present invention to provide an economically advantageous method for preventing concrete structure from cracking. [0015] In order to solve the above problems, the present invention employs the following means. That is, the concrete structure according to claim 1 is prevented from cracking.
The method is applied to the construction of a concrete structure including a preceding concrete structure and a following concrete structure arranged adjacent to each other via a joint surface, and the generation of cracks inside the concrete structure. A method for preventing cracking of a concrete structure, wherein a first water circulating unit disposed on the preceding concrete structure, a second water circulating unit disposed on the succeeding concrete structure, A first connection pipe that supplies water circulated through the water circulation section to the first water circulation section, and a second connection pipe that supplies water circulated through the first water circulation section to the second water circulation section. wherein the the second connecting tube, Fei the cooling unit is provided for cooling the water flowing therein
Using the crack prevention device, the preceding concrete structure
Until the temperature of the following concrete structure matches,
While the water is being cooled by the crack prevention device,
Cross between cleat structure and subsequent concrete structure
It is characterized by circulating. [0016] To be configured as described above, according to the cracking prevention method of the concrete structure, the trailing co
Heated by heat of hydration accumulated inside concrete structure
By supplying the drained water to the preceding concrete structure, it is possible to reduce the temperature difference generated between the two, and to improve the effect of suppressing the occurrence of cracks in the subsequent concrete structure as compared with the conventional case Is possible. The ratio
Pre-concrete while cooling water with crack prevention device
Between the concrete structure and the subsequent concrete structure
By reducing the temperature of both the leading and trailing concrete structures, it is possible to reduce the period until the temperatures of the leading and trailing concrete structures coincide with each other compared to the conventional method. Can be
The time required for operating the device can be reduced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1, the cracks preventing method according to an embodiment of the present invention, cracking proof
Underground continuous wall (concrete structure) using the stopping device 11
12 is a diagram showing an example of a case where the method is applied when constructing No. 12. FIG. The underground continuous wall 12 includes a preceding element (preceding concrete structure) 13 and a succeeding element (following concrete structure) both having a reinforced concrete structure.
14 are alternately connected to each other. The construction of the underground continuous wall 12 is performed in the following procedure. That is, first, a plurality of preceding elements 13 are constructed at intervals in the ground. Next, the ground between these preceding elements 13 is excavated, and the succeeding element 14 is constructed there, and the preceding element 13 and the following element 14 are integrated. Since the above-described construction method is employed, a joint surface 15 is formed between the preceding element 13 and the following element 14. On the other hand, as shown in the figure, the crack preventing device 11 includes first and second water circulation portions 16 and 17 and a first connection pipe 19 (19a, 19) for connecting between them.
b, 19c), a second connecting pipe 20, and a pump P, a cooling unit 21, and a flow meter F provided in the middle of the second connecting pipe 20. The first connecting pipe 19 is composed of 19a disposed on the underground continuous wall 12 side and 19b and 19c disposed on the second connecting pipe 20 side.
In each of a, 19b, and 19c, water flows in the direction from the following element 14 to the preceding element 13 (the direction A in the drawing). Furthermore, the ends of 19 b and 19 c are connected to the second connection pipe 20. On the other hand, the second connection pipes 20 and 20 have water inside the second connection pipes 20 and 20 from the preceding element 13 to the following element 14.
(Direction B in the figure). The cooling unit 21 includes a heat dissipating mechanism and a blowing mechanism (not shown).
A configuration in which the water flowing between the second connecting pipes 20 and 20 can be cooled by circulating the water flowing between the second connecting pipes 20 by circulating the water inside the heat dissipation mechanism and forcing air into the air by the blowing mechanism. It has been. Further, the first and second water circulation sections 16,
Numeral 17 is embedded in each of the preceding and succeeding elements 13 and 14, and includes a plurality of cooling pipes (pipes) 2 both.
, 22,... Are provided. The cooling pipes 22, 22,... Are reinforced baskets 23, 23 constituting the preceding and following elements 13, 14, respectively.
Are fixed to the first connecting pipes 19a, 19b, 19c via flexible hoses 26, 26,. FIG. 2 is a view showing a situation when the underground continuous wall 12 is viewed from a vertical cross section orthogonal to the extending direction (p direction in FIG. 1). As shown in the figure, the cooling pipe 22 goes from the upper end 12a to the lower end 12b of the underground continuous wall 12,
The configuration is again toward the upper end 12a. Thus, in the first water circulation section 16, the water supplied from the first connection pipe 19a is supplied to the cooling pipe 2
2, circulates inside the underground continuous wall 12 and flows to the first connection pipe 19 b, and in the second water circulation unit 17, water supplied from the first connection pipe 19 c Flows through the cooling pipe 22 to the first connection pipe 19a. Next, the crack preventing device 11 was used.
Explanation of crack prevention method for underground continuous wall 12
I do. In the succeeding element 14 immediately after the concrete is poured, the heat of hydration of the concrete is accumulating, so that the temperature rises in the interior. On the other hand, at this time, the preceding element 13 has been cooled to some extent because the time has elapsed since the concrete was poured. Therefore,
In the vicinity of the joint surface 15 inside the succeeding element 14, a temperature gradient occurs. If the temperature gradient is left untreated, the concrete forming the following element 14 shrinks and causes temperature cracks. Therefore, the operation of the crack prevention device 11 is started. By the operation of the crack preventing device 11, the water heated by the following element 14 is supplied from the second water circulating section 17 to the first water circulating section 16, and this water is further supplied to the preceding element 13. The heat is deprived and is again supplied to the succeeding element 14 side. Thereby, the heat inside the succeeding element 14 is transferred to the preceding element 13, and the temperature difference between the preceding and succeeding elements 13 and 14 is reduced. Also,
At this time, by adjusting the operation of the pump P while referring to the flow meter F, the first and second water circulating units 16 and
The flow rate of the water flowing through 17 is made appropriate so that the temperature difference between the preceding and succeeding elements 13 and 14 can be effectively reduced. At the same time as circulating such water, the cooling unit 21 is driven to cool the water supplied from the first water circulating unit 16 to the second water circulating unit 17. Thus, the trailing element 14, cooled water is supplied, so that the temperature rise of the trailing element 14 is suppressed. Moreover, in this way, since the water that has been cooled to a trailing element 14 is supplied, the water supplied to the preceding element 13 side from the trailing element 14 side, of course the temperature is lower than the conventional And therefore ,
Since a rise in the temperature of each of the following elements 13 and 14 is suppressed, a temperature difference generated between them can be reduced as compared with the related art. Prior to such a method for preventing cracking,
FIG. 3 is a graph showing the effect of reducing the temperature difference between the succeeding elements 13 and 14 and the effect of suppressing the temperature rise of the preceding element 13. In the graph shown in FIG. 3, the horizontal axis represents the period after the concrete was poured into the succeeding element 14, and the vertical axis represents each of the preceding and following elements 1.
3 and 14 represent temperatures within. In the figure,
The solid line represents the temperature change of the succeeding element 14, and the two-dot chain line represents the temperature change of the preceding element 13. In the drawing, reference numeral 1 denotes a temperature change situation when no piping or the like is applied to the succeeding element 14, and reference numeral 2 denotes the conventional crack preventing device 1 shown above.
Is a temperature change situation when the above is applied to the underground continuous wall 12. Further, reference numeral 3 denotes a temperature change when the above-described crack prevention device 11 is applied to the underground continuous wall 12. As can be seen from these, when no action is taken (reference numeral 1), the leading / following element 13,
14 is 30 ° C. or more at the maximum, and even when the conventional crack prevention device 1 is applied (reference numeral 2),
The temperature difference between the succeeding elements 13 and 14 is 10 to 1 at the maximum.
Although the temperature is about 5 ° C., the present embodiment prevents cracking.
According to the method, the temperature difference between the preceding and succeeding elements 13 and 14 can be made 10 ° C. or less. Further, in the conventional crack preventing device 1, it takes 9 to 10 days to equalize the temperatures of the preceding and succeeding elements 13 and 14, whereas according to the crack preventing method of the present embodiment,
The temperature of the preceding and succeeding elements 13 and 14 can be made the same in 5 to 6 days. Further, according to the crack prevention method of the present embodiment, the maximum temperature of the preceding element 13 can be reduced by nearly 10 ° C. as compared with the conventional crack prevention device 1. As described above, the present embodiment prevents cracks.
According to the method, it is provided between the second connection pipes 20, 20 for supplying water from the first water circulation section 16 to the second water circulation section 17 .
In order to circulate the water while cooling it with the cooling unit 21,
It is possible to suppress a temperature rise in both the preceding and succeeding elements 13 and 14. Thereby, the temperature difference generated between the two can be reduced as compared with the conventional case, and the occurrence of cracks in the succeeding element 14 can be suppressed. Also, as described above, the leading / following element 1
In order to suppress the temperature rise of both the first and second elements 13 and 14,
For a short period of time (5 in the above example)
６6 days), and the time required for operating the apparatus can be reduced to about １ ／. As a result, the crack preventing device 11 can be prevented within a certain construction period as compared with the related art.
, The pump P, the flow meter F, the cooling unit 21, and the first and second connection pipes 19, 20 and the like can be easily reused sequentially at different construction locations, which is economically advantageous. is there. For example, the cycle of excavation and concrete placement of an underground continuous wall is usually about 10 days, whereas according to the crack prevention method of the present embodiment, only about half the operation period is required. Even if construction is performed simultaneously at two places in the same site, it is sufficient to prepare a set of the pump P, the flow meter F, the cooling unit 21, the first and second connection pipes 19 and 20, and the like. Become. As described above, even when there are a plurality of construction sites, it is not always necessary to prepare devices corresponding to the number of construction sites, and each component of the device can be used more economically than in the past. Further , according to the method for preventing cracking, it is possible to suppress the rise in temperature of the preceding element 13 as described above.
Since the deformation due to the temperature rise of 3 is constrained by the surrounding ground, there is no need to worry about the occurrence of stress, cracks and the like inside the preceding element 13. In the above embodiment, other configurations are adopted for the structure of each part of the crack prevention device 11 and the structure to which the crack prevention device 11 is applied, without departing from the scope of the present invention. You may do it. For example, the cooling section 21 does not need to be an air-cooled type as described above , but may be a type using a refrigerant or the like. Further, the method for preventing cracking of the present invention
Only applicable to construction of underground diaphragm wall as in the above embodiment
When constructing other concrete structures such as dams
It is also applicable. As described above, the method for preventing cracking of a concrete structure according to the present invention is directed to a method for preventing a concrete structure from being cracked by providing a cooling portion to a second connecting pipe for supplying water from a first water circulating portion to a second water circulating portion. To
Using the crack prevention device provided, the concrete structure ahead
Until the temperature of the body and the following concrete structure match.
While the water is being cooled by the crack prevention device,
Cross between cleat structure and subsequent concrete structure
As a result, the temperature rise in both the preceding and following concrete structures can be suppressed. As a result, the temperature difference generated between the two can be reduced, and the effect of suppressing the occurrence of cracks in the subsequent concrete structure can be improved as compared with the related art. In addition, since the rise in temperature of both the leading and following concrete structures can be suppressed in this manner, the period until the temperatures of the leading and trailing concrete structures coincide with each other is shortened as compared with the related art. And the time required for operating the apparatus can be shortened. This makes it easy to sequentially reuse the components of the crack prevention device at different construction locations within a certain construction period, and the device can be used more economically than in the past. In addition, since the rise in temperature of the preceding concrete structure can be suppressed as described above, the deformation due to the rise in temperature of the preceding concrete structure is restrained by the surrounding ground, and stress and cracks, etc. Does not occur. Therefore, a more excellent effect of preventing cracking than in the prior art can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view schematically showing one embodiment of the present invention, and schematically shows a crack preventing device and an underground continuous wall (concrete structure) to which the device is applied. FIG. 3 is a plan view showing a configuration. FIG. 2 is an elevational sectional view showing a situation when the crack prevention device and the underground continuous wall (concrete structure) shown in FIG. 1 are viewed in a section orthogonal to the extending direction of the underground continuous wall. FIG. 3 shows a method for preventing cracks according to an embodiment of the present invention.
6 is a graph showing the effect of reducing the temperature difference between the preceding and following elements (preceding and following concrete structures) by the method. FIG. 4 is a perspective view showing a conventional apparatus for preventing cracking of a concrete structure according to the present invention. [Description of Signs] 11 Anti-cracking device 12 Underground continuous wall (concrete structure) 13 Previous element (preceding concrete structure) 14 Following element (following concrete structure) 15 Joint surface 16 First water circulation section 17 Second water circulation units 19a, 19b, 19c First connection pipe 20 Second connection pipe 21 Cooling unit 22 Cooling pipe (piping)

Claims (1)

(57) In the construction of the Claims 1] beating joint surface of concrete structures constructed and a trailing concrete structures and prior concrete structure disposed adjacent to each other via <br Applied to prevent cracking of concrete structures applied to prevent the occurrence of cracks inside the concrete structures
A method , comprising: a first water circulating unit disposed on the preceding concrete structure; a second water circulating unit disposed on the subsequent concrete structure; and water circulated through the second water circulating unit. a first connection pipe for supplying the first water circulation unit comprises a second and a connecting tube for supplying water to circulate the first water circulation portion in the second water circulation portion, the second connecting pipe the cracking proof cooling unit is provided for cooling the water flowing therein
The preceding concrete structure and the following concrete structure using a stopping device
Until the temperature of the two matches,
While cooling the water, the preceding concrete structure and the following concrete
Circulating between the concrete structure
A method for preventing concrete structures from cracking.