JPH06294017A - Steel fiber for concrete reinforcement - Google Patents

Abstract

PURPOSE:To produce a practical concrete-reinforcing steel fiber having simple structure and excellent dispersibility and capable of improving the original concrete-reinforcing effect. CONSTITUTION:The steel fiber to be mixed in concrete to reinforce the concrete. It has a vertically elongated flat cross-section having a width/thickness ratio of >=2 and a total length/width ratio of >=20 and <50 and has bent parts at both ends or in the total length in the plane of the flat face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concrete-reinforcing fiber used for the purpose of being mixed with concrete to reinforce its strength.

[0002]

2. Description of the Related Art Concrete used in the field of civil engineering and construction shows high strength against compression, but its tensile strength is about 1/10 of the compression strength, so it easily cracks and collapses at once. There is a drawback that Reinforcing bars and steel wires have been used as reinforcements to compensate for these drawbacks.
In recent years, steel fiber reinforced concrete (SFR) in which steel fibers having a diameter of 0.4 to 1.0 mm and a length of 25 to 80 mm are mixed into concrete at a volume ratio of about 0.3 to 2% to concrete (SFR
C) has been widely used, and in order to improve the adhesion of such steel fiber to concrete, both ends are bent, or irregular shaped parts are continuously attached as in Japanese Patent Publication No. 1-232178. Alternatively, it is used after being bent into a corrugated shape as in Japanese Patent Publication No. 55-16768.

[0003]

However, while the deformation and bending of the steel fibers improve the adhesion to the concrete, the so-called fiber ball formation phenomenon in which the fibers are entangled with each other tends to occur and the dispersibility is impaired. There is a problem.
As a result, the workability at the time of adding the steel fiber to the concrete is significantly impaired, and in an extreme case, it is necessary to use a disperser for the addition. Furthermore, during the mixing of concrete,
The steel fibers that have been thrown in become fiber balls again,
There was a problem that a sufficient reinforcing effect could not be obtained or the amount of mixture could not be increased. As a method for preventing the entanglement of the steel fibers before being put in, as disclosed in Japanese Patent Publication No. Sho 60-9976, a method has been proposed in which water-soluble resins are used to bond or bundle the fibers together like staples. However, there are problems such as increased cost, resin that has melted into the concrete to change the slump of the concrete, and management of rain leak of the material before input. In addition, increasing the amount of steel fiber mixed to obtain high concrete strength causes a large increase in cost and the workability of concrete (handlability before placing such as slump) is impaired. It has been desired to develop steel fibers that can provide a high reinforcing effect with a mixed amount. The present invention was created in order to solve the above-mentioned problems, and an object thereof is to have a simple structure, good dispersibility, and at the same time improve the original concrete reinforcing effect. The purpose is to provide a practical steel fiber for concrete reinforcement.

[0004]

In order to achieve the above object, the present invention has a longitudinally flat cross section and a width / thickness of 2 or more and a total length / width of 20 or more and less than 50.
The configuration is such that both ends or the entire length has bent portions in the same plane as the flat surface. Preferably the bend is 1 / width
2 or more, reduced diameter 0.4-1.0 mm, length 20
-80 mm and tensile strength in the range of 100-150 kgf / mm ² .

[0005]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 4 show examples of steel fibers for concrete reinforcement according to the present invention. 1 is a steel fiber according to the present invention, which is preferably made by drawing a steel wire rod to a predetermined diameter and then biasing it with a die, a press, a rolling roll, or the like, and having a converted diameter calculated from a cross-sectional area. 0.4 ~
1.0mm, length 20 ~ 80mm, tensile strength 100
It is in the range of up to 150 kgf / mm ² . As shown in FIG. 1, the steel fiber 1 has a vertically long flat cross section. (a) has upper and lower parallel straight surfaces 11 and 12, and left and right parallel straight surfaces 13 and 14.
(B) shows the left and right parallel straight planes 13 and 14
And the upper and lower surfaces are curved surfaces 11′12 ′ that are continuous from the parallel straight surfaces 13 and 14. In (c), the left and right sides are gentle curvature surfaces 13 'and 14', and the upper and lower sides are steep curvature surfaces 11 "and 12".

Further, in the present invention, in addition to flattening the cross-sectional shape of the steel fiber, the relationship between the width dimension w, the thickness dimension t and the length dimension 1 is a constant condition. That is, the width dimension w / thickness dimension t (width / thickness ratio) is 2 or more, and the length dimension 1 / width dimension w (width aspect ratio) is 20 or more and less than 50. If the ratio w / t is less than 2, fiber balls are likely to occur, which is unsuitable, and it is effective to have a large value such as 4 to 5, but if w / t is too large, the thickness becomes thin. The upper limit is about 8 because the fiber may be deformed during kneading of concrete. As the length of the fiber becomes shorter, the reinforcing effect is reduced accordingly, so that l / w is required to be at least 20 in order to secure the minimum length. However, if l / w is too large, entanglement occurs even if w / t is appropriate.
The upper limit must not exceed 50.

Further, the steel fiber 1 according to the present invention has a bent portion 100 for improving the adhesion to concrete, and the bent portion 100 is the same as a flat surface as shown in FIGS. 2 to 4. It is formed as an in-plane bending, that is, a vertical bending, and must not be a right angle, that is, a lateral bending with respect to the plane as shown in FIG. Explaining the reason for this, the width aspect ratio is substantially increased by bending in the same plane as the flat surface in this way, and the dispersibility in concrete is improved by the synergistic effect with the width aspect ratio. It is possible to further improve. Bending in the same plane as the flat surface also exerts a remarkable effect in terms of reinforcing action. That is, the concrete reinforcing effect of the steel fiber having the bent portion increases as the steel fiber slip-out resistance that occurs during the concrete crack generation process increases. That is, a shape having a larger resistance when the bent portion is deformed into a straight line has a higher reinforcing effect. Since the deformation resistance is proportional to the second moment of area of the fiber, the shape bent in the same plane as the flat surface as described above has an extremely large deformation resistance and a high reinforcing effect can be obtained. For example, the second moment of the round steel wire fibers having a diameter of 0.8 mm (officially: πd ^4/64) and, in terms of diameter 0.8 mm (width w1.6mm made of the same material, thickness t0.4m
When sectional comparing the second moment (official wh ^3/12) when the height 1.6mm bent flat fibers m), the following Table 1
It is as follows.

[0008]

[Table 1]

From Table 1, when the in-plane bending (longitudinal bending) is the same as that of the flat surface, about 16
It can be seen that the deformation resistance is twice as great.

Bending portion 100 that is bent in the same plane as this flat surface
May be applied to both ends or the middle of the fiber in the longitudinal direction, or may be applied to the entire length, and the shape is arbitrary. In FIG. 2, the bent portion 100 is formed in a trapezoidal shape so that the straight portions 101, 101 are left at both ends. Figure 3 shows a straight part 1 in the middle
The mountain-shaped bent portions 100, 100 are formed at both ends so that 01 is left. In this case, the two peaks may be upside down and opposite. FIG. 4 shows a bent portion 1 in a wavy shape over the entire length.
00 is formed. However, in any case, the bending height h needs to be 1/2 or more of the width w.
This is because it is indispensable for enhancing the adhesiveness, dispersibility, and deformation resistance with concrete described above. If the width w is less than 1/2, even if the width / thickness ratio and the width aspect ratio are proper, it is expected. Can not be obtained. Bending in the same plane as the flat surface is performed by rolling a round wire manufactured by wire drawing with a roll to flatten it, and then bending with a grooved roll for preventing tilting, or bending into a round wire. It can be obtained by flattening with a rolling roll after applying.

Next, concrete examples of concrete reinforcing steel fibers according to the present invention and test results of characteristics will be shown. JIS G 35
5.5m of mild steel wire rod (SWRM6) specified in 05
Steel with 4 types of vertical cross-sections, made from mφ as a raw material, drawn to a diameter of around 1 mmφ, flattened, then longitudinally bent, and cut to a specified length. Fabricated fiber. The sectional shape is shown in FIG. 1 (b) and the bent portion shape is shown in FIG. For comparison, a steel fiber as drawn (round wire) was also made. The dimensions are shown in Table 2. NO.2 to NO.6
Each steel fiber had the same cross-sectional area as the round wire 0.8 mmφ, and the bending height h and the length l were all the same. After kneading these steel fibers in a 1.0 ton concrete mixer for 15 minutes, the dispersibility was evaluated by the number of fiber balls formed (a state in which 10 or more steel fibers were entangled was counted as a fiber ball). The results of the tests are shown in Table 2.

[0012]

[Table 2]

As is clear from Table 2, NO.5 having a width / thickness ratio of 2 or more and a width aspect ratio of less than 50.
It can be seen that with No. 6 and No. 6, no fiber balls were generated and the dispersibility was good.

Next, steel fibers having various bending heights were manufactured by the same material and manufacturing method as described above. They are shown in Table 3 as NO.7-NO.10. No. 10 is a bending type which is bent on a surface perpendicular to the pressure surface, that is, a lateral bending type shown in FIG. In order to examine the reinforcing effect, each steel fiber was mixed into fresh concrete in a volume ratio of 0.4%, sufficiently kneaded with a mixer for 1.0 ton and uniformly dispersed, and then 150 × 150
A fiber-reinforced concrete test piece of × 530 mm was manufactured.
Since the amount of steel fibers mixed in was small, no fiber balls were formed in any of the steel fibers. After the concrete test piece was cured in water for 28 days, a bending test was carried out to obtain a bending strength and a so-called bending toughness represented by an area surrounded by a bending load and a bending curve. The results are shown in Table 3.

[0015]

[Table 3]

As is apparent from Table 3, NO.6 to NO.9
Comparing No. 8 and N, the bending height is less than 1/2 of the width
O.9 has a lower reinforcing effect than NO.6 and NO.7, which are the scopes of the present invention. Especially, the bending toughness is low. Bending height is the same as 2.0mm NO.1,3,6
Comparing No. 6, the reinforcing effect decreases in the order of NO.6,3,1 and agrees with the order of magnitude of w / t (second moment of area). It can be seen that a high reinforcing effect can be obtained by setting w / t to a large value, and a w / t value of 2 or more is suitable in consideration of dispersibility. Comparing NO.6 and NO.10, it can be seen that the reinforcing effect of NO.6 is also excellent, and that bending is performed with vertical bending, which is the same surface as flat pressing, which shows a high reinforcing effect.

[0017]

According to the present invention described above, a cross section having a width / thickness of 2 or more and a total length / width of 20 to 50 has a vertically long flat shape, and both ends or the entire length are in the same plane as the flat surface. Since it has a bent part, the width aspect ratio is substantially large and the left and right sides are flat, so when it is put into concrete it separates smoothly and has good dispersibility, and entanglement during kneading hardly occurs. Become. Therefore, a disperser is not required at the time of addition, and fiber balls are not generated, so that the amount of mixing into concrete can be increased and homogeneous concrete can be obtained. Further, the width-thickness ratio is large, the second moment of area is large, and the bending resistance is so large that the bending resistance is so-called vertical bending, so that the reinforcing effect is enhanced. For this reason, when obtaining concrete of the same strength, it is possible to use a small amount of mixing, which is highly economical, and the small amount of mixing makes it possible to obtain an excellent effect that fiberballing becomes more difficult to occur. To be

[Brief description of drawings]

1 is a cross-sectional view of a steel fiber for concrete reinforcement according to the present invention.

FIG. 2 is an enlarged perspective view showing an example of a reinforcing fiber according to the present invention.

FIG. 3 is an enlarged perspective view showing another example of the reinforcing fiber according to the present invention.

FIG. 4 is an enlarged perspective view showing another example of the reinforcing fiber according to the present invention.

FIG. 5 is a perspective view of a comparative product.

[Explanation of symbols]

 1 Steel fiber 100 Bending part w Width t Thickness h Bending height

Claims (3)

[Claims] 1. A steel fiber for mixing with concrete to reinforce its strength, the cross section having a vertically long flat shape, the width / thickness of 2 or more, and the total length / width of 20 or more and less than 50. A fiber for concrete reinforcement, characterized in that it has bent portions at both ends or the entire length in the same plane as the flat surface. 2. The bending height is 1/2 or more of the width.
The fiber for reinforcing concrete as described in. 3. The steel fiber for concrete reinforcement according to claim 1, wherein the drawn steel wire is pressure-biased and bent.