JP7162988B2 - Crack control method - Google Patents

Description

The present invention relates to a method for controlling cracking in concrete.

Floors of factories, warehouses, parking lots, etc. are constructed by laying gravel, crushed stone, etc. on the ground, tamping them, and placing concrete thereon. Tensile stress is generated inside concrete due to heat of hydration of cement, temperature change due to external temperature, drying shrinkage, etc. When the tensile stress exceeds the allowable tensile stress of concrete, cracks occur.

When an opening or the like exists in a concrete floor or the like and an internal corner occurs, stress concentration occurs in that portion, a large tensile force is generated, and cracks are likely to occur there.

Therefore, in order to prevent cracks from entering corners, a technique has been proposed in which cutter joints are formed in a diamond shape around a column (see, for example, Patent Document 1).

JP-A-7-62754

However, in the above-described conventional technique, there is a problem in that the cutoff from the surrounding earthen floor concrete is insufficient, and it is difficult to stop the propagation of cracks. In order to prevent this, it is possible to post-cast the concrete inside the rhombus and cut off the edges from the surrounding dirt floor concrete, but there was a problem that construction required time and effort.

The present invention has been made in view of the above problems, and is a method for controlling cracks in concrete, wherein each corner of a structure having a polygonal cross-section is curved before pouring concrete. A method is provided that includes forming joints extending from each corner of the structure along each side of the structure after covering with a covering member or placing concrete.

According to the present invention, the trouble of post-casting concrete can be saved, and cracking of concrete around the structure can be suppressed.

The figure explaining the crack of concrete. The figure explaining the 1st method of controlling the crack of concrete. The figure which illustrated the cross section which formed the joint. The figure which illustrated the place where the joint was formed. The flowchart which showed the construction procedure by a 1st method. The figure explaining the 2nd method of controlling the crack of concrete. The figure which illustrated the covering member used by the 2nd method. The figure which illustrated the position of the joint formed by a 2nd method. The flowchart which showed the construction procedure by a 2nd method.

Concrete (earth floor concrete) to be constructed on the floor surfaces of factories, warehouses, parking lots, etc. is cast after a structure such as a pillar is installed, or is cast after the part is cut into a square box. FIG. 1( a ) is a top view of the floor concrete placed. In FIG. 1(a), pillars 10 having a polygonal cross section, in this case, a rectangular cross section, are installed at regular intervals, and dirt floor concrete 11 is placed around the pillars 10. In FIG.

Since the dirt floor concrete 11 is not cast in the portion where the column 10 exists, the portion of the column 10 becomes the opening 12 as shown in FIG. 1(b). For this reason, the dirt floor concrete 11 has four corner portions (internal corners) 13 recessed inward corresponding to the four protruding corner portions formed by the adjacent side surfaces of the pillar 10 .

After being placed, the dirt floor concrete 11 is cured and hardened to exhibit a predetermined strength, but shrinkage occurs in the process. During this shrinkage, tensile stress is generated inside the concrete. Such stress concentrates on cutouts, corners, cavities, areas where the cross section changes abruptly, and the like. Therefore, when a corner portion such as the internal corner 13 is generated, stress concentration occurs at that portion.

When stress concentration occurs, tensile forces tend to pull in opposite directions centering on that portion, and cracks are more likely to occur there. When it exceeds the allowable tensile stress of the concrete, from the corner 15 formed by two adjacent sides 14 of the column 10, as shown in FIG. A crack 16 extending in an oblique direction is generated. This occurs not only in the earth floor concrete 11, but also in the slabs and the like that constitute the floors of each floor of buildings in which the columns are made of steel frames with rectangular cross sections.

Since the crack 16 extending obliquely from the corner 15 is generated due to the presence of the internal corner 13 where stress concentration occurs as described above, it is possible to suppress the generation by eliminating the internal corner 13 . A specific method therefor will be described in detail below.

FIG. 2 is a diagram illustrating a first method for eliminating the internal corner 13. As shown in FIG. The first method is to install a structure having a polygonal cross-section such as an RC (reinforced concrete) column or a steel frame column, place earth floor concrete, and then perform construction.

In the first method, as shown in FIG. 2( a ), after installing the pillar 10 and placing the earth floor concrete 11 , the joints are devised and different from each corner 15 of the pillar 10 . A joint 20 is formed so as to extend in the direction. The joint 20 can be formed by cutting the hardened concrete to a predetermined depth using a road milling machine with a blade that rotates at high speed called a road cutter.

FIG. 3 illustrates a cross section in which the joint 20 is formed. The depth of the joint 20 is about 1/3 of the thickness t of the earth floor concrete 11 . Cracks can be concentrated in the joint 20 by forming the cracks to such a depth. Note that the depth of the joint 20 may be deeper than t/3. If a reinforcing bar is buried at a position shallower than t/3 in the earth floor concrete 11, the joint 20 is formed by cutting the reinforcing bar together.

The dirt floor concrete 11 is formed by laying crushed stones 21 or the like on the ground, tamping and flattening the ground, pouring dump concrete 22, placing reinforcing bars as necessary, and then pouring. The dirt floor concrete 11 may be placed after laying the crushed stone 21 or the like and tamping it.

Referring to FIG. 2(a) again, since it is difficult to form a joint 20 with a road cutter near the pillar 10, a small cutter (such as a hand grinder) that can be handled by hand is used to cut the joint 20 up to the pillar 20. A joint 20 is formed. By forming the joint 20 up to the edge of the pillar 20, the internal corner 13 can be eliminated.

The joint 20 can be formed so as to extend from one corner 15 along each of the two side surfaces 14 forming the corner 15 . As a result, cracks can be concentrated on the joint 20, and the occurrence of cracks in the oblique direction from the corner 15 can be suppressed.

However, in this case, as shown in FIG. 4, two joints 20 are formed from one corner 15, and the number of joints 20 increases. Therefore, the joints 20 can be formed so as to extend from the corners 15 of the pillar 10 in different directions. When the formed joint 20 is viewed from above, it has a swastika shape as shown in FIG. 2(b). By forming such a swastika shape, it is sufficient to form one joint 20 from one corner 15, so the number of joints 20 to be formed can be reduced.

If the distance between the pillars is 5 m or less, only the joints 20 extending in different directions from the corners 15 should be formed. If the distance between the pillars exceeds 5 m, it is desirable to separately form the necessary number of joints 20 between the pillars so that cracks are concentrated in the formed joints 20 .

When a plurality of pillars 10 are installed, joints 20 are formed to connect the pillars alternately on the right and left sides as shown in FIG. If so, linear joints 20 are formed at appropriate intervals between the columns. In this manner, the joints 20 are formed in a grid pattern at substantially regular intervals.

FIG. 5 shows the construction procedure according to the first method. Starting from step 100, in step 101, crushed stone or the like is laid on the ground, tamped down, and dump concrete is cast, and then columns 10 as structures are installed. The pillar 10 may be constructed by using precast concrete, a steel frame pillar, or by arranging reinforcing bars, building a formwork, and pouring concrete.

In step 102, earth floor concrete 11 is placed. The dirt floor concrete 11 is placed on the dump concrete. At step 103, it waits for the earth floor concrete 11 to harden.

At step 104, a road cutter or grind cutter is used to form joints 20 extending from each corner 15 of the column 10 in different directions. Then, joints 20 are also formed at other locations as required, and the work is finished at step 105 .

FIG. 6 is a diagram illustrating a second method for eliminating the internal corner 13. As shown in FIG. The second method is to install a structure having a polygonal cross section, such as an RC (reinforced concrete) column or a steel frame column, and perform construction before pouring the earthen floor concrete.

In the second method, after installing the pillar 10 as a structure, each corner 15 of the pillar 10 is covered with a covering member 30 having a curved surface. After that, earth floor concrete 11 is placed and buried. If the covering member 30 is long in its longitudinal direction and protrudes from the surface of the dirt floor concrete 11, the protruding portion is removed by cutting or the like.

The covering member 30 is a circular processing member having an arcuate cross section, and as shown in FIG. 7, is produced by cutting a hollow cylindrical member such as a vinyl chloride pipe, a void pipe, or a steel pipe at two points along its length. be. In the case of the pillar 10 having a rectangular cross section, since the corners 15 have an angle of about 90°, a circular processing member can be obtained by cutting (halving) the side surface of the hollow cylindrical member, for example, in half. Obtainable. The halving is an example, and the cutting ratio is not limited to about 1/2. The circular processing member has an opening at the cut portion and constitutes an insertion opening 31 for inserting the corner portion 15 .

The covering member 30 has a curved surface with a constant curvature on the outer surface in contact with the dirt floor concrete 11, and accommodates the corners 15 of the pillars 10 inside, so the internal corners 13 can be eliminated. As a result, it is possible to suppress the occurrence of cracks extending obliquely from the corners 15 . Concrete is placed also inside the covering member 30, and the inside is filled with concrete. Also, the interior of the covering member 30 may have any structure as long as it can accommodate the corner portion 15 of the pillar 10 .

A second method may be to simply install the covering member 30, but this only suppresses the occurrence of cracks extending obliquely from the corner 15, and there is a possibility that cracks will occur in other portions.

Therefore, joints 20 can be provided at appropriate intervals and cracks can be concentrated on the joints 20 as in the conventional art. The joints 20 may be provided so as to extend in different directions from the respective corners 15 of the pillar 10 as shown in FIG. It may be provided so as to extend outward from the central portion of the side surface. In addition, the position in which the joint 20 is provided is not limited to these examples.

FIG. 9 shows the construction procedure by this method. Starting from step 200, in step 201, crushed stone or the like is laid on the ground, tamped down, and dump concrete is cast, and then columns 10 as structures are installed. The pillar 10 may be constructed by using precast concrete, a steel frame pillar, or by arranging reinforcing bars, building a formwork, and pouring concrete.

At step 202 , a covering member 30 is installed to cover each corner 15 of the pillar 10 . At step 203, the dirt floor concrete 11 is placed. The dirt floor concrete 11 is placed on the dump concrete. At this time, concrete is placed inside the covering member 30 as well. At step 204, it waits for the earth floor concrete 11 to harden.

At step 205, the joint 20 is formed using a road cutter. Once the joint 20 has been formed, the operation ends at step 206 . Although the joint 20 is formed in step 205 here, the joint 20 may not be formed.

By providing such a method, it is possible to save the time and effort of post-casting around structures such as pillars, and to cast earthen floor concrete all at once. Also, no cracks extending obliquely from the corners of the structure occur. Furthermore, since it is not necessary to provide diamond-shaped joints around the structure, it is effective in terms of design, and the number of joints to be constructed can be reduced.

Although the method of the invention has been described in detail with reference to the embodiments shown in the drawings, the invention is not limited to the embodiments described above, but can be modified in other embodiments, additions, modifications, It can be changed within the range that a person skilled in the art can conceive, such as deletion, and as long as the action and effect of the present invention are exhibited in any aspect, it is included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10... Column 11... Dirt floor concrete 12... Opening part 13... Inner corner 14... Side surface 15... Corner part 16... Crack 20... Joint 21... Crushed stone 22... Scrap concrete 30... Covering member 31... Insertion opening

Claims (4)

A method for controlling cracking in concrete comprising:
Before placing the concrete, a structure having a polygonal cross section is installed, each corner of the installed structure is covered with a covering member having a curved surface, or the structure is installed and installed. forming joints extending from each corner of said structure along each side of said structure after pouring said concrete around said structure. The covering member is obtained by cutting a hollow cylindrical member in the length direction in order to accommodate each corner of the structure inside, has an insertion opening into which the corner is inserted, and has a circular cross section. 2. The method of claim 1, wherein the plurality of arcuate circular processing members. 3. The method according to claim 1, further comprising the step of forming a joint after covering with said covering member and placing said concrete. 2. The method of claim 1, wherein forming the joint extending from each corner of the structure forms the joint in a different direction from each corner.

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