ARCHED STEEL FIBERS FOR REINFORCING CEMENT-BASED MATERIAL

Abstract

The present invention discloses an arched steel fiber for reinforcement of a cement-based material, of which a main body is arched in a length direction and opposite ends of the main body are curved such that the steel fiber has a higher pullout resistance strength compared to a conventional steel fiber, thereby improving mechanical performance such as a tensile strength, a flexural strength, an energy absorption capability, and the like of a cement compound. In addition, compared to a conventional art, a mixing amount of steel fiber to performance can be reduced so that an added economic value in terms of consumable cost can be created

Claims

1. An arched steel fiber for reinforcement of a cement-based material, comprising an arched main body having a curvature radius and curved and straight ends respectively provided at opposite ends of the main body, wherein the curved ends are bent in a direction that is opposite to a direction that the main body is arched, and the straight ends are continued to the curved ends, respectively.

2. The steel fiber for reinforcement of the cement-based material of claim 1, wherein the curvature radius R of the main body is 5 mm to 80 mm

3. The steel fiber for reinforcement of the cement-based material of claim 1, wherein a total length of the main body, the curved ends, and the straight ends is 10 mm to 90 mm, a tensile strength is 500 to 2800 MPa, and a tensile elastic coefficient is 200 GPa or more.

4. The steel fiber for reinforcement of the cement-based material of claim 1, wherein an angle of the curved end is 30 ° to 160°.

5. The steel fiber for reinforcement of the cement-based material of of claim 1, wherein a length of the straight end is 0.5 mm to 10 mm

Description

DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows arched steel fiber for reinforcement of a cement-based material according to a first exemplary embodiment of the present invention.

[0022] FIG. 2 shows arched steel fiber for reinforcement of a cement-based material according to a second exemplary embodiment of the present invention.

[0023] FIG. 3 shows arched steel fiber for reinforcement of a cement-based material according to a third exemplary embodiment of the present invention.

[0024] FIG. 4 and FIG. 5 are graphs that show results of a pullout test performed on the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention.

[0025] FIG. 6 is a graph that shows a result of a bending test performed on the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention.

[0026] FIG. 7 shows steel fiber for reinforcement of a cement-based material according to a conventional art.

MODE FOR INVENTION

[0027] Hereinafter, a technical configuration of arched steel fiber for reinforcement of a cement-based material according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0028] First, as shown in FIG. 1 to FIG. 3, arched steel fiber for reinforcement of a cement-based material according to an exemplary embodiment of the present invention includes an arched main body 10 and predetermined curved ends 11 and 11a and straight ends 12 and 12a that are respectively provided at opposite ends of the main body 10.

[0029] The curved ends 11 and 11a and the straight ends 12 and 12a are respectively integrally provided at the opposite ends of the main body 10. That is, the curved portions 11 and 11a are formed with a predetermined angle α and the straight ends 12 and 12a are formed with a predetermined length l.sub.e, respectively, at the opposite ends of the main body 10.

[0030] The arched main body 10 provides stronger pullout resistance strength compared to a conventional art, and ultimately, provides a technical effect of improving mechanical performance such as tensile strength, flexural strength, energy absorption capability, and the like of the cement composite.

[0031] In particular, the curved ends 11 and 11a of the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention are bent in a direction that is opposite to the arch-shape of the main body 10.

[0032] In this case, the straight portions 12 and 12a are respectively extended from the curved portions 11 and 11a.

[0033] The arched main body 10 may have a predetermined curvature radius R. For example, the curvature radius R of the main body 10 may have various values between 5 mm and 80 mm. Here, a straight length of the steel fiber may be changed depending on the arch curvature radius R of the main body 10.

[0034] A total length of the steel fiber, that is, the total length of the main body 10, the curved ends 11 and 11a, and the straight ends 12 and 12a, may be set within a range of 10 mm to 90 mm to obtain a tensile strength of 500 MPa to 2800 MPa and a tensile elastic coefficient of 200 GPa or more.

[0035] When the curvature radius R of the main body 10 is 5 mm or less, the entire size of the steel fiber is reduced so that it is difficult to expect elasticity from the arched shape, and when curvature radius R of the main body 10 exceeds 80 mm, an elastic synergistic effect of the plurality of steel fibers may be deteriorated due to the total length.

[0036] The angle α of the curved ends 11 and 11a may vary within a range of 30° to 160°.

[0037] In addition, the length l.sub.e of the straight ends 12 and 12a may preferably be set to be within a range of 0.5 mm to 10 mm.

[0038] Here, The angle α of the curved ends 11 and 11a or the length l.sub.e of the straight ends 12 and 12a has a close relationship with mechanical adhesion performance in concrete when the arched steel fiber is mixed with a corresponding cement-based material.

[0039] When the angle α of the curved ends 11 and 11a is less than 30° or exceeds 160°, or when the length l.sub.e of the straight ends 12 and 12a is less than 0.5 mm, the mechanical adhesion performance in the corresponding concrete is only somewhat enhanced. Further, when the length l.sub.e of the straight ends 12 and 12a is set to be longer than 10 mm, unnecessary waste of materials may occur.

Exemplary Embodiment 1

[0040] In order to determine adhesion performance of the arched steel fiber for the cement-based material according to the exemplary embodiment of the present invention, a pullout test was performed on the arched steel fiber for the cement-based material according to the exemplary embodiment of the present invention and conventional hook-type steel fiber for the cement-based material.

[0041] In order to perform the pullout test, a dog-bone-shaped mortar specimen was divided into two portions according to JCI SF-8, and then a steel fiber was embedded 25 mm into each center of the divided portions.

[0042] Compression strength of the mortar was 30 MPa, and steel fibers used in the pullout test each had a tensile strength of 1300 MPa, a diameter of 0.75 mm, and a length of 60 mm.

[0043] In manufacturing of the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention, a curvature radius R of the arch was set to 35 mm, the angle α of the curved ends 11 and 11a was set to 90°, and the length l.sub.e of the straight ends 12 and 12a was set to 1.5 mm.

[0044] Results of the pullout test, as shown in the graph of FIG. 4, shows that a maximum pullout load of the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention is improved by 115% compared to the conventional steel fiber for reinforcement and a pullout resistance strength after the maximum pullout load is improved by 125%.

[0045] A result of observation of the surface of the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention shows that friction marks with a cement matrix remain all over the embedded length of the steel fiber, but in case of the conventional steel fiber for reinforcement, the friction marks remain only in a hook portion. Accordingly, it can be determined that the entire length of the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention resists the pull-out.

Exemplary Embodiment 2

[0046] In order to determine adhesion performance according to the length l.sub.e of the straight lines 12 and 12a of the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention, a pullout test was performed with the length l.sub.e of the straight lines 12 and 12a as a variable.

[0047] A pullout test method, an embedment length, and a compression strength of mortar were set to be the same as those of Exemplary Embodiment 1, and steel fibers used in the pullout test were prepared with a tensile strength of 1300 MPa, a diameter of 0.75 mm, and a length of 60 mm. The lengths l.sub.e of the straight ends 12 and 12a were respectively set to 0, 1.5 mm, 2.5 mm, and 3.5 mm.

[0048] As shown in the results of the pullout test, represented by the graph of FIG. 5, maximum pullout loads of the straight ends 12 and 12a were improved by 437%, 450%, and 575%, respectively, when the lengths l.sub.e of the straight ends 12 and 12a were set to 1.5 mm, 2.5 mm, and 3.5 mm, respectively, with reference to 0 mm of the length l.sub.e of the straight ends 12 and 12a, and pullout resistance strengths after the maximum pullout loads were improved by 102%, 110%, and 122%, respectively.

Exemplary Embodiment 3

[0049] In order to determine bending performance of concrete reinforced by the arched steel fiber according to the exemplary embodiment of the present invention, bending performance was tested on the arched steel fiber, the conventional hook-type steel fiber, and circular-shaped steel fiber.

[0050] A specimen used in the test was manufactured as a 150 mm×150 mm×550 mm specimen having a prismatic shape, and a third-point bending test was performed according to JSCE-SF4.

[0051] Table 1 shows a mixing ratio of concrete for determination of bending performance, and steel fiber that has the same specification as of the arched steel fiber of Exemplary Embodiment 1 for the pullout test and the hooked-type steel fiber were applied, and in the case of the circular-shaped steel fiber, the tensile strength was 1300 MPa, the diameter was 0.75 mm, and the interior diameter was 30 mm. A mixing amount was 30 kg/m.sup.2.

TABLE-US-00001 TABLE 1 Unit material amount (kg/m.sup.3) High performance AE Design Coarse Air water standard aggregate amount S/a W/C reducing Compression Maximum (%) (%) (%) Fine Coarse agent strength size Water Cement aggregate aggregate (standard) (MPa) (mm) (W) (C) (S) (G) (AD) 24 25 5 47.8 47.1 173 367 846 924 5.32

[0052] Compression strength was measured after being aged for 28 days, and a result of the measurement shows that the conventional hook-type steel fiber, the circular-shaped steel fiber, and the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment satisfied the design standard compression strength.

[0053] As shown in the graph of FIG. 6, a bending test result shows that flexural strength of concrete reinforced with the conventional hook-type steel fiber was 4.045 MPa, flexural strength of concrete reinforced with the conventional circular-shaped steel fiber was 4.178 MPa, and concrete reinforced with the arched steel fiber of the present invention was 4.302 MPa, and equivalent flexural strengths were respectively 2.751 MPa, 1.709 MPa, and 3.057 MPa, respectively.

[0054] That is, compared to the conventional hook-type steel fiber and the conventional circular-shaped steel fiber, flexural strength of the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention was improved by 6.35% and 2.97%, and the equivalent flexural strength was improved by 11.1% and 78.9%.

[0055] In the concrete reinforced with the arched steel fiber for reinforcement of the cement-based material according to the exemplary embodiment of the present invention and in the concrete reinforced with the conventional hook-type steel fiber, deflection of the specimen and weight loss did not significantly occur after the first crack. However, in the case of the concrete reinforced with the circular-shaped steel fiber, the specimen was deflected and load loss significantly occurred as the steel fiber rupture occurred after the first crack.

[0056] Hereinabove, the arched steel fiber for reinforcement of the cement-based material was described as an exemplary embodiment of the present invention for convenience of description, however, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.