KR102530816B1 - Double-Arch Steel Fiber - Google Patents

Abstract

The present invention includes a first arch portion having a convex shape toward a first direction; a second arch portion having a convex shape toward a second direction opposite to the first direction and having the same radius of curvature as the first arch portion; a connecting portion connecting one end of the first arch portion and one end of the second arch portion and forming an inclination gradient; a first bent portion connected to the other end of the first arch portion and bent in the first direction; a second bent portion connected to the other end of the second arch portion and bent in the second direction; a first closing portion bent in the second direction at an end of the first bent portion; It relates to a double-arch steel fiber comprising a; second finishing portion bent in the first direction at the end of the second bent portion.

Description

Double-arch steel fiber {Double-Arch Steel Fiber}

The present invention relates to a double-arch steel fiber for reinforcing building materials or civil engineering materials. It is an invention about

In general, concrete members have excellent compressive strength, durability and rigidity, but have low tensile strength, bending strength, impact strength and energy absorption capacity. According to these characteristics, concrete members have a high possibility of failure when subjected to tensile or dynamic loads.

In order to solve the above problems, a method of improving physical properties such as tensile strength, impact resistance, and peeling resistance by mixing steel fibers for concrete reinforcing in a concrete member is widely used.

In general, steel fibers for concrete reinforcement have a steel material processed into a fiber form. When steel fibers having a relatively short length are evenly dispersed in concrete members, physical properties such as tensile strength, flexural strength and shear strength of concrete can be improved. In addition, it can be a means to increase resistance to cracks because it has a strong impact resistance.

In order for the steel fibers to be bonded to the concrete to exhibit the above physical properties, the steel fibers must be evenly dispersed in the concrete and must be well adhered to the concrete paste with high adhesion to the concrete. In addition, the steel fiber must have a material with high tensile strength against external stress.

Looking at the conventional steel fiber technology, there is a hooked ends type steel fiber in which both ends are bent in a straight steel fiber having a circular cross section disclosed in Korean Patent Publication No. 2013-0129385. In addition, Korean Patent Registration No. 1,403,659 uses a ring-shaped steel fiber with both ends spaced apart.

In addition to the above examples, there are a number of examples of steel fibers for improving bending toughness by reducing the rebound rate during pouring after being incorporated into shotcrete and preventing pull-out after pouring.

Such conventional steel fibers for concrete reinforcement have been most often applied to shotcrete, which is a secondary support material during tunnel excavation. In addition, it is commonly used in places such as floor slabs where reinforcement of steel bars is difficult due to its small cross section and crack control is required.

In the case of steel fibers applied to shotcrete, the size is about 0.5 to 0.55 mm in diameter and 30 to 35 mm in length, whereas the size of steel fibers reinforced in floor slabs is 0.75 to 0.90 mm in diameter and 50 to 60 mm in length.

Conventional end-hook type steel fibers are generally formed into a hook shape by bending both ends of a straight body at a predetermined angle. In the case of using such a shape, when the steel fiber is pulled out of the concrete by the tensile force acting after the occurrence of cracks, the strength of the pull-out resistance is rapidly reduced due to poor adhesion in straight parts other than the hook part. For this reason, when using end-hook type steel fibers, there is a critical limitation in improving the mechanical performance of concrete members.

In order to solve these limitations, technologies implementing various features are disclosed in Korean Patent Registration No. 1,073,393 and the like.

However, even in the case of the above techniques, there is a problem that the energy absorption is not sufficient for the tensile force acting on the concrete.

Republic of Korea Patent Publication No. 2013-0129385

The present invention has been conceived from the above problems of the prior art, and has the advantage of having a sufficient amount of energy absorption for the tensile force acting on the concrete by including a pair of arch structures symmetrical to the shape of the steel fiber body.

In addition to this, the steel fiber of the present invention has the advantage of achieving uniformity of physical properties by uniform dispersion as well as ensuring rust prevention performance.

As a means for achieving the above object, the double-arch steel fiber of the present invention (hereinafter referred to as “steel fiber of the present invention”) includes a first arch portion having a convex shape toward a first direction; a second arch portion having a convex shape toward a second direction opposite to the first direction and having the same radius of curvature as the first arch portion; a connecting portion connecting one end of the first arch portion and one end of the second arch portion and forming an inclination gradient; a first bent portion connected to the other end of the first arch portion and bent in the first direction; a second bent portion connected to the other end of the second arch portion and bent in the second direction; a first closing portion bent in the second direction at an end of the first bent portion; It characterized in that it includes; a second closing portion bent in the first direction at the end of the second bent portion.

As an example, the connection part, the first closure part, and the second closure part are characterized in that the same inclination gradient is formed.

As an example, the connection part, the first closure part, and the second closure part are characterized in that they are composed of the same length.

As an example, it is characterized in that both sides are symmetrical in opposite directions from the center of the connection part.

As an example, a coating layer containing alkoxysilane, zinc, and silicate is further formed on the outer periphery.

As an example, the coating layer may further contain alkyl phosphate and ammonium sulfate.

The steel fiber of the present invention has the advantage of improving the resistance to pulling out by having a structure including a symmetrical arch, etc., and thus, in the cement composite containing the steel fiber of the present invention, the tensile strength, bending strength, and energy absorption capacity are improved. It has the advantage of improving the same mechanical performance.

In addition, it has the advantage of being able to improve physical properties such as strength in cement composites by improving adhesion strength by controlling cracks at the interface between steel fibers and paste, as well as exhibiting anti-rust function in cement composites.

1 is a cross-sectional side view showing a steel fiber of the present invention;
2 is a side cross-sectional view showing the shape of each embodiment,
Figure 3 is a graph showing the experimental results of the maximum pull-out load and energy absorption according to each embodiment shown in Figure 2,
4 is a graph showing experimental results of maximum pulling load and energy absorption for other embodiments.

Hereinafter, the configuration and operation of the present invention will be described in more detail based on the accompanying drawings. In describing the present invention, the terms or words used in this specification and claims are based on the principle that the inventor can appropriately define the concept of the term in order to best describe his or her invention. should be interpreted as a meaning and concept that corresponds to the technical idea of

As shown in FIG. 1, the steel fiber 1 of the present invention includes a first arch portion 2 having a convex shape toward the first direction; a second arch portion (3) having a convex shape toward a second direction opposite to the first direction and having the same radius of curvature as the first arch portion (2); a connecting portion 4 connecting one end of the first arch portion 2 and one end of the second arch portion 3 and forming an inclination gradient; a first bent portion 5 connected to the other end of the first arch portion 2 and bent in the first direction; a second bent portion 6 connected to the other end of the second arch portion 3 and bent in the second direction; a first closing portion 7 bent in the second direction at an end of the first bent portion 5; It is characterized in that it includes; a second closing portion (8) bent in the first direction at the end of the second bent portion (6).

The steel fiber 1 of the present invention can be used to reinforce building materials and/or civil engineering materials, and can be particularly used to reinforce cement-based materials. In addition, it can be used to reinforce interior and exterior materials for construction.

By uniformly dispersing steel fibers in concrete, it is possible to improve tensile strength, flexural strength, resistance to cracking, toughness, shear strength and impact resistance. In addition, it is possible to improve economic feasibility, constructability and safety by having an effect of eliminating the need for installation work of wire mesh or reinforcing bars.

In order to improve the performance of a member through steel fibers, each steel fiber must be well attached to the concrete inside the member, and as a result, the member made of the two materials must have an integral behavior. The adhesion of steel fibers to concrete is called adhesion, and how well the adhesion is achieved can be expressed through a measure of adhesion strength.

As the steel fibers are more strongly attached to concrete, the properties of the reinforced concrete member incorporated with the steel fibers can also be improved.

In FIG. 1, the straight line length (L) may mean the maximum value of the distance that the steel fiber 1 of the present invention has in the longitudinal direction. That is, the straight length L of the steel fiber 1 of the present invention may be the straight line distance between the ends of the first closure 7 and the second closure 8.

In addition, in the steel fiber 1 of the present invention, as shown in FIG. 1, the average resistance length (Lt) may mean the length of the steel fiber 1 when the steel fiber 1 of the present invention is straightly stretched. That is, the average resistance length (Lt) may be a value obtained by dividing the volume of the steel fiber 1 by the cross-sectional area of the steel fiber 1.

First of all, the steel fiber 1 of the present invention is characterized by having a pair of arch shapes, the first arch portion 2 having a convex shape toward the first direction and the second direction opposite to the first direction. It has a shape convex toward the direction, and it is characterized in that the second arch portion (3) having the same curvature radius as the first arch portion (2) is included.

The radius of curvature R1 of the first arch portion 2 and the radius of curvature R2 of the second arch portion 3 are the same, and only the direction is convex in opposite directions in the first and second directions. It is characterized by consisting of.

The connecting portion 4 connects one end of the first arch portion 2 and one end of the second arch portion 3 to form an inclination gradient.

An arch in the opposite direction is also formed at the ends of the first arch portion 2 and the second arch portion 3, for which it is connected to the other end of the first arch portion 2 and bent in the first direction. The first bent part 5 and the first closure part 7 bent in the second direction at the end of the first bent part 5 are formed, so that the first bent part 5 and the first closure part 7 An arch is formed in the first direction by ), and is connected to the other end of the second arch portion 3 and is bent in the second direction at the second bent portion 6 and the end of the second bent portion 6 An arch is formed in the second direction by the second closing portion 8 bent in the first direction.

On the other hand, when tensile force acts on the concrete containing the steel fiber 1 of the present invention and deformation occurs in the steel fiber 1 by the tensile force, the maximum pulling load and energy absorption rate of the steel fiber 1 is the straight length of the steel fiber 1 (L), the average resistance length (Lt) of the steel fiber (1) and the characteristics of the curved portion of the body of the steel fiber (1).

Since the steel fibers are attached and hardened inside the concrete, when a force is applied to the concrete and/or the steel fibers, stress may occur between the surface of the steel fibers and the concrete. Therefore, if the surface area of the steel fiber is large, a greater adhesion force can occur for the same stress.

Even if the steel fiber has the same linear length (L), the steel fiber with a longer average resistance length (Lt) can have a larger surface area. Steel fibers with a larger surface area may have stronger adhesion to concrete.

Also, when the steel fiber is pulled in both directions, the steel fiber is subjected to a force that straightens it. If the steel fiber has a curved shape, the resistance of the steel itself against the tensile force that tends to straighten the steel occurs. The resistance to deformation can absorb energy due to the tensile force acting on the concrete.

Therefore, the steel fiber (1) of the present invention is characterized by having two symmetrical arch shapes, and the steel fiber (1) of the present invention has a longer average resistance length (Lt) compared to the straight length (L). can That is, it can have the effect of increasing the surface area, and can also have the characteristic of increasing the adhesive force acting between the steel fiber and the concrete.

In particular, in the steel fiber 1 of the present invention, as shown in FIG. 1, the connecting portion 4, the first finishing portion 7, and the second finishing portion 8 have the same inclination gradients α1, α2, and α3. characterized by the formation of

By this configuration, as shown in the following experimental examples, a higher energy absorption rate can be formed.

In addition, the steel fiber 1 of the present invention is characterized in that the connection part 4, the first closure part 7, and the second closure part 8 are composed of the same length (d1, d2, d3).

By this configuration, as shown in the following experimental examples, a higher energy absorption rate can be formed.

In addition to this, the steel fiber 1 of the present invention is characterized in that both sides are symmetrical in opposite directions at the center of the connection part 4. This structure has the effect of improving the bending toughness capability in all directions structurally.

Hereinafter, with reference to FIGS. 2 and 3, experimental results of maximum pulling load and energy absorption according to embodiments of the steel fiber 1 of the present invention will be described.

Experiments according to the embodiments were conducted in a pull-out test method, and the tensile force was applied in both directions of the concrete by including each embodiment inside the concrete specimen. Through this experiment, the maximum tensile load acting on the steel fibers included in the concrete can be measured.

In addition, through this experiment, the displacement of the members due to the tensile force acting on the steel fibers included in the concrete can be measured.

Accordingly, as shown in FIG. 3, a load-displacement graph may be obtained by experiments according to embodiments. The vertical axis represents the maximum pulling load acting on the steel fiber, and the horizontal axis represents the deformation of the steel fiber. The energy absorbed by the steel fiber can be obtained through the area of the graph.

In this experiment, the embodiments are shown in FIG. 2, and in the case of (a), the connection part 4, the first closure part 7, and the second closure part 8 are composed of the same length (d1, d2, d3). However, the inclination gradient (α2) of the connection part (4) is configured differently from the inclination gradients (α1, α3) of the first closure part (7) and the second closure part (8), and in the case of (b), the connection part (4) ), the inclination gradients (α1, α2, α3) of the first closure part 7 and the second closure part 8 are the same, but the length d2 of the connection part 4 is different from the first closure part 7 and It is configured differently from the lengths (d1, d3) of the second closing part (8), and in the case of (c), the connection part (4), the first closing part (7) and the second closing part (8) have the same length (d1 , d2, d3) and the same gradients (α1, α2, α3).

As the experimental results are shown in FIG. 3, it can be seen that the pulling force and energy absorption rate are derived in the order of (c) > (b) > (a). Therefore, the most advantageous result is that the connecting part 4, the first finishing part 7 and the second finishing part 8 are configured with the same lengths d1, d2, d3 and the same slopes α1, α2, α3. It can be seen that is derived.

On the other hand, in the present invention, an example in which a coating layer is formed on the outer periphery is proposed, so that the coating layer is formed on the body made of steel and the outer periphery of the body.

The coating layer is characterized in that it includes an alkoxysilane, zinc, silicate.

The alkoxysilane is an inorganic binder, represented by the general formula RnSi(OR')4-n (wherein R is an alkyl group having 1 to 8 carbon atoms, R' represents an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms) Representative examples of alkoxysilanes include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, and n-propyltriethoxysilane. Toxyl silane, phenyl trimethoxy silane, phenyl triethoxy silane, etc. are mentioned.

The zinc serves to prevent corrosion.

However, the zinc component reacts with cement to expand, and cracks may occur at the interface due to this expansion.

Accordingly, an example is presented in which silicate is further included in the coating layer of the present invention. By including silicate so that a tight paste is formed at the interface, cracks generated as described above are also filled, causing only zinc to be added. This is to ensure that any issues that may arise are controlled.

The silicate generates calcium silicate hydrate through a reaction with calcium hydroxide generated during cement alkali reaction, and the generated calcium silicate hydrate is filled in the micropores of the paste so that the crack surface is filled tightly, so that cracks and voids are firmly filled. to reinforce this.

Preferably, the coating layer is appropriately formulated to contain 30 to 100 parts by weight of zinc and 5 to 10 parts by weight of silicate based on 100 parts by weight of alkoxysilane.

In addition to this, in the present invention, an example in which alkyl phosphate and ammonium sulfate are further included in the coating layer in addition to the above compositions is presented.

In the process of storing and mixing steel fibers, static electricity is generated due to mutual friction, which can cause cohesion between steel fibers or cohesion with other components, which can act as a factor that hinders uniform dispersion. In the coating layer of the present invention, alkyl phosphate is added to control the aggregation between steel fibers so that the physical properties are uniformly expressed.

In addition to this, ammonium sulfate is further added to the coating layer, and ammonium sulfate controls cracks caused by curing heat by absorbing curing heat generated during the curing process of the coating layer.

These cracks can act as a point that inhibits rust prevention and can act as a factor that lowers the adhesion at the interface, so microcracks are controlled by the addition of ammonium sulfate. At the same time, ammonium sulfate doubles the effect of controlling the generation of static electricity by alkyl phosphate.

That is, by adding ammonium sulfate, the conductivity of the alkyl phosphate is further doubled to increase the aggregation control efficiency.

Preferably, 0.1 to 1 part by weight of alkyl phosphate and 0.1 to 1 part by weight of ammonium sulfate are blended with respect to 100 parts by weight of alkoxysilane.

Hereinafter, with reference to FIG. 4, the experimental results of the maximum pulling load and energy absorption according to the embodiments of the steel fiber 1 of the present invention will be described.

Even in this case, the experiments according to the embodiments were conducted in a pull-out test method, and the tensile force was applied in both directions of the concrete by including each embodiment inside the concrete specimen.

In this experiment, in Example 1, the same steel fiber as (c) was used in the experiment, and a coating layer containing 80 parts by weight of zinc based on 100 parts by weight of alkoxysilane was applied to the outer periphery. In the case of Example 2, in the above experiment The same steel fiber as in (c) was used, and a coating layer containing 80 parts by weight of zinc and 5 parts by weight of silicate was applied to the outer circumference of the outer periphery, based on 100 parts by weight of alkoxysilane. Steel fibers were used, and a coating layer containing 80 parts by weight of zinc, 5 parts by weight of silicate, 0.1 part by weight of alkyl phosphate, and 0.1 part by weight of ammonium sulfate was applied to the outer periphery thereof based on 100 parts by weight of alkoxysilane.

As the experimental results are shown in FIG. 4, it can be seen that the pulling force and energy absorption rate are derived in the order of Example 3> Example 2> Example 1.

The fact that Example 2 showed better results in terms of pulling force and energy absorption than Example 1 was determined to be due to tight filling of cracks and voids at the interface according to the addition of silicate, and Example 3 had the best results. It is believed that the derivation of is due to the uniform physical properties secured by the addition of alkyl phosphate and ammonium sulfate and the enhancement of adhesion by controlling microcracks in the coating layer.

1: steel fiber
2: first arch
3: 2nd arch
4: connection part
5: first bent part
6: second bent part
7: 1st closing part
8: 2nd closing part

Claims (6)

a first arch portion having a convex shape toward a first direction;
a second arch portion having a convex shape toward a second direction opposite to the first direction and having the same radius of curvature as the first arch portion;
a connecting portion connecting one end of the first arch portion and one end of the second arch portion and forming an inclination gradient;
a first bent portion connected to the other end of the first arch portion and bent in the first direction;
a second bent portion connected to the other end of the second arch portion and bent in the second direction;
a first closing portion bent in the second direction at an end of the first bent portion; and
And a second closing portion bent in the first direction at the end of the second bent portion,
A double-arch steel fiber, characterized in that a coating layer containing alkoxysilane, zinc, and silicate is further formed on the outer periphery.
According to claim 1,
The double-arch steel fiber, characterized in that the same inclination gradient is formed in the connecting part, the first finishing part and the second finishing part.
According to claim 2,
The double-arch steel fiber, characterized in that the connection part, the first closure part and the second closure part are composed of the same length.
According to claim 3,
Double-arch steel fiber, characterized in that both sides are symmetrical in the opposite direction at the center of the connection.
delete According to claim 1,
The double-arch steel fiber, characterized in that the coating layer further contains alkyl phosphate and ammonium sulfate.

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