JPH0132178B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to steel fibers mixed in for the purpose of reinforcing the strength of concrete.

(Conventional technology) Just as there has been the practice of reinforcing clay walls by adding straw to them since ancient times, in recent years the technology of using composite materials has begun to emerge, and conventional individual materials have completely failed to do so. Many materials with new characteristics such as so-called composite materials are appearing.

Therefore, in contrast to concrete, which is used as a civil engineering construction material and is inexpensive and has many advantages, but also has the fatal flaw of being brittle and prone to cracking, we decided to use steel with a diameter of 0.4 to 0.6 mm and a length of 20 to 60 mm. Approximately 1 to 2% fiber by volume (80 to 160 by weight)
It was discovered that steel fiber-reinforced concrete (hereinafter referred to as "reinforced concrete") with high tensile strength and extremely high toughness can be obtained by mixing Kg/m ³ ), and this reinforced concrete is also expected to be put into full-scale practical use. Many research and developments are being carried out on steel fiber manufacturing technology, construction technology, and application development.

By the way, when converting the amount of steel fiber to be mixed into concrete based on the above volume ratio in actual work, the unit volume of concrete (1 m ³ ) is
The amount of steel fiber that must be mixed into each piece reaches 80 to 160 kg.
Actual concrete pouring requires a large amount of steel fiber.

Now, the role of reinforcing steel fibers in ordinary concrete that is not prestressed is to first adhere to the concrete and then share the load acting on the concrete, making it difficult for the concrete to crack and preventing the concrete from breaking. It is intended to be difficult.

Structures that have been developed in recent years in which concrete is reinforced with steel fibers are basically based on the above idea, but when steel fibers are used as reinforcement materials, they are much more integrated with the concrete than when ordinary reinforcing bars are used. As a result, expectations were focused on absorbing as much energy as possible during fracture, in other words, demonstrating high toughness as a structure.

In particular, the Japan Society of Civil Engineers' Steel Fiber Reinforced Concrete Design and Construction Guidelines (draft) states that steel fiber reinforced concrete is a composite material that overcomes the brittleness of concrete and has significantly improved toughness.

Furthermore, the Japanese Industrial Standards (JIS G3112 - Steel Bars for Reinforced Concrete) stipulates the irregular shapes of deformed reinforcing bars for concrete, but of course there are no regulations regarding steel fibers that generally have a diameter of 1 mm or less.

Deformed reinforcing bars can be processed by hot rolling, so
The projected overhang area (hereinafter referred to as overhang area) of the knot (unusual shaped part) is large in comparison to the tensile strength.

For deformed reinforcing bars b/t=0.16A~0.32A/30~40 For steel fibers b/t=0.2A~0.5A/70~130 where t: tensile strength (Kg/ ^mm2 ) b: overhang Area (mm ² ) Furthermore, since deformed reinforcing bars are used in long lengths, the total projected overhang area becomes enormous.

Steel fiber is a short material, and its aspect ratio, which represents the ratio of its total length to its diameter, is used as an indicator of performance.

For these reasons, it is clear that the technology for deformed reinforcing bars cannot be used as a reference for studying the deformed shapes of steel fibers.

However, regarding the irregular shape of steel fibers, it is not clear how much protrusion is preferable and what should be done to improve toughness. Currently, it is not produced.

(Object of the Invention) The present invention provides the above-mentioned irregular shape of the steel fiber.
In particular, with the aim of improving the toughness of concrete, the shapes of steel fibers created by wire drawing and cutting can be obtained with various surface shapes by processing them into different shapes using forming rollers. This was done by focusing on the fact that it has the ability to change its toughness (work to break), tensile strength, bending strength, etc. at will, and aims to provide high-performance steel fibers. be.

(Background of the invention) In the case of general reinforcing bars, the adhesion performance with concrete is usually determined by the combination of the adhesion strength with the concrete on the cylindrical surface and the bearing strength with the concrete at the joints (overhanging parts). It is considered.

In the case of steel fibers, where toughness is an issue, it is necessary to increase the energy absorption after the structure is destroyed. It is best to slowly pull it out while resisting.

From the above, it is necessary that the irregularly shaped portion of the steel fiber has an overhang that is more than necessary for bearing pressure resistance, and an overhang that is less than necessary to prevent the steel fiber from being cut.

From this, when the tensile strength of the steel fiber is low, the steel fiber breaks quickly, so there is not much need for overhangs, and when the tensile strength of the steel fiber is high, the number of overhangs is large (long steel fibers). It turned out to be more effective.

(Structure of the Invention) Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a perspective view of a steel fiber obtained by wire drawing and cutting.

In the figure, 1 indicates a base portion, and 2 indicates an irregularly shaped portion.

The base portion 1 and the irregularly shaped portion 2 appear alternately, the total length of the steel fiber is indicated by L, the diameter is indicated by d, and the pitch at which the irregularly shaped portion 2 appears is indicated by P.

FIGS. 2a and 2b are cross-sectional views taken along lines aa and bb in FIG. 1.

Therefore, the surface that provides bearing resistance of concrete from one direction within one pitch of the above-mentioned steel fibers, that is, Fig. 2a
The overhanging area b, which is the sum of S1 and S2 in the middle and S0 in Fig. 2b, is expressed by the following formula.

b=S1+S2+S0 Further, the sum of the overhanging areas at all pitches over the entire length of the steel fiber, that is, the total bearing pressure area B, is determined by the following equation.

B=b×L/P Figure 3 shows some steel fiber specimens with different machining depths in the irregularly shaped part, and the volume ratio of these specimens is 1.0%.
2 is a chart showing the results obtained by preparing a mortar prismatic column mixed with the above method, measuring the area of the load-deflection curve in a bending test of the prismatic column, and determining the area as a substitute characteristic for absorbed energy.

FIG. 4 is a characteristic diagram showing the relationship between the overhang area b of the above sample and the absorbed energy in the bending test.
The figure is also a characteristic diagram showing the relationship between the total overhang area B and the absorbed energy in the bending test.

Based on the test results of the above sample, first, if we were to determine the preferred range of the overhang area b, it would be 0.2A≦b≦0.5A, where the cross-sectional area of the base portion 1 is Amm. It's important.

Furthermore, for toughness, the sum of the same overhang areas B
Also, long steel fibers with shallow processing or long pitches tend to be better than short steel fibers with deep processing or small pitches.

Therefore, the aspect ratio (L/
When d) is between 60 and 100, the average absorbed energy value is 78, and outside this range it is 64.

In addition, for pitch, when P is in the range of 4d to 10d for the fiber diameter d, the average value of absorbed energy is 86,
Outside this range, it will be 75.

Next, FIG. 6 shows the relationship between the tensile strength T of steel fibers, the sum total B of the overhang area, and toughness.

FIG. 7 is a characteristic diagram showing the relationship between the total overhang area B and toughness, and FIG. 8 is a conceptual diagram showing the relationship between the total overhang area B--tensile strength T--toughness.

Moreover, FIG. 9 is a characteristic diagram showing the relationship between the tensile strength σf of steel fibers and the sum B of the overhanging areas.

In FIG. 9, the conventional thin plate sheared straight type steel fiber (without deformation processing) is in the region a in the figure, and the preferable range for the steel fiber of the present invention is in the range b.

After all, when comparing the conventional type steel fiber and the steel fiber of the present invention, it is found that the steel fiber of the present invention has a high tensile strength and a high adhesion strength.

In addition, as for how to determine the absorbed energy in the bending test, as shown in Figure 10a, the sample is
The area A surrounded by the diagonal line in Figure 10b, which shows the load-deflection curve when loading at two equal points
(Kg-mm) was determined, and this was taken as the absorbed energy.

Here, the amount of deflection is a constant value of 1/150 of the distance between the supporting points.

In addition, in the above explanation, the irregularly shaped portion of the steel fiber is processed flatly from the same direction, but for practical steel fibers, the irregularly shaped part is processed from both sides simultaneously or alternately. Furthermore, the basic cross-sectional shape may be square, hexagonal, or other cross-sectional shapes other than circular.

(Effects) The present invention aims to improve the toughness of steel fibers obtained by wire drawing and cutting by shaping the steel fibers. The preferred range was determined from the ratio of the cross-sectional area of the section and the irregularly shaped section, and by mixing the steel fibers of this invention into concrete, the load acting on the concrete after adhering to the concrete. This product is designed to maximize the distribution of energy and minimize the occurrence of cracks in the concrete, making it difficult for the concrete to break.It exhibits excellent action and effects that maximize the requirements required of steel fibers, and is extremely practical. It is possible to present reinforced concrete with high strength.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a perspective view of steel fibers, and FIGS. 2a and 2b are views of FIGS.
Figure 3 is a characteristic diagram of the steel fiber specimen, Figure 4 is a characteristic diagram showing the relationship between overhang area and bending test absorbed energy, Figure 5
Figure 6 is a characteristic diagram showing the relationship between the total overhang area and energy absorbed in bending tests, Figure 6 is a diagram showing the relationship between the tensile strength of steel fibers, the total overhang area, and toughness, and Figure 7 is a graph showing the relationship between the total overhang area and toughness. A characteristic diagram showing the relationship between the sum total and toughness, Figure 8 is a conceptual diagram of the relationship between the total sum of overhang area - tensile strength - toughness, Figure 9 is a characteristic diagram showing the relationship between the total sum of overhang area and Figures 10a and 10b are an explanatory diagram of a bending test and a diagram of a deflection curve. 1... Base part, 2... Irregular shape part.

Claims (1)

[Scope of Claims] 1. Consisting of steel fibers obtained by wire drawing and cutting, an unprocessed base portion and a deformed portion that extends outward by press deformation processing and have the same cross-sectional shape are alternately formed. In continuous steel fibers for concrete reinforcement, the projected overhanging area bmm ² of the irregularly shaped part with respect to the cross-sectional area Amm ² of the base part satisfies the relationship 0.2A≦b≦0.5A, and the aspest ratio (steel fiber total length/diameter) A steel fiber for concrete reinforcement characterized by having a tensile strength of 60 to 100. 2. The steel fiber for concrete reinforcement according to claim 1, wherein in the steel fiber, the total projected overhang area Bmm ² of each irregularly shaped portion over the entire length of the steel fiber satisfies the relationship 3A≦B≦8A. 3 In the steel fibers, the total projected overhang area B
The steel fiber for concrete reinforcement according to claim 1, wherein mm ² and axial tensile strength TKg satisfy the relationship of 0.02T≦B≦0.08T.