JPH0550459B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to the improvement of steel fibers mixed into concrete materials to improve various properties of concrete. (Prior Art) Concrete used as a civil engineering and construction material has the disadvantage that it is strong in compression but weak in tension and bending, and is brittle and prone to cracking. In order to improve these drawbacks of concrete, steel fibers are mixed with concrete and poured. Traditionally, steel fibers used for this purpose have a diameter of 0.3
~0.6mm, length of about 20-40mm short fibers, uniformly mixed into concrete at 0.5-2% by volume will improve concrete's tensile, bending, and shear strengths, and will also improve crack restraint properties. Can be made into excellent steel fiber reinforced concrete. In order to increase the reinforcing effect of steel fibers, the ratio of their length l to diameter d, i.e. aspect ratio l/d
It is necessary to appropriately select No. 195044/1983 discloses steel fibers whose aspect ratios are increased from 60 to 100 by examining the surface shape of the steel fibers based on these relationships. (Problem to be solved by the invention) In order to properly and fully exhibit the reinforcing effect of steel fibers in any steel fiber reinforced concrete, it is necessary to
In addition to selecting the shape and dimensions of the steel fibers, the problem is how to uniformly disperse the steel fibers in the concrete material during concrete mixing. Concrete is manufactured by mixing sand, aggregate, cement, water, etc. in a mixer, but the steel fibers added to this mix tend to become entangled, forming lumps called fiber balls, which prevent uniform mixing. To prevent the formation of fiber balls, loosen steel fibers using a special disperser or the like and rain them down to mix into the concrete material being mixed. However, dispersing and mixing steel fibers using a dispersing machine requires the dispersing machine to be installed at the concrete placement site, which requires installation space and cost, and it takes a long time to mix the concrete. This results in an increase in concrete placement costs. Generally, the dispersion and kneading properties of steel fibers for concrete reinforcement are influenced by the aspect ratio l/d.
If it is smaller than 50, uniform dispersion is possible without using a dispersing machine or other feeding machine, but the reinforcing effect is low, and on the other hand, steel fibers with high reinforcement strength with l/d of 60 to 100 or more cannot be dispersed. They are under the contradictory conditions of not being sexually active. The present invention solves the above-mentioned problems of the prior art, does not reduce the concrete reinforcing effect of steel fibers, and its dispersibility is so good that no special dispersing machine is required, thereby making it possible to mix steel fiber reinforced concrete. The purpose of the present invention is to provide steel fibers for reinforcing concrete that can shorten time and reduce casting costs. (Means for Solving the Problems, Effects, and Examples) The object of the present invention is to change the structure of the steel fiber for concrete reinforcement by alternating the unprocessed part and the processed irregularly shaped part on the base part with a circular cross section at a required pitch. In addition, at least one end is formed with a bent part, and the aspect ratio determined by the total length in the longitudinal direction / diameter is in the range of 30 to 60, and is created by processing the irregularly shaped part and forming the bent part. If the sum B of the projected area in the longitudinal direction is the cross-sectional area of the base part A, then 3A≦B≦12A
This is achieved by making sure that the longitudinal projected overhang area caused by processing the irregularly shaped part is less than 1.95A. The adhesion of steel fibers to concrete is influenced by the surface shape of the steel fibers. For this reason, when a protruding portion formed by processing the steel fiber into a different shape is provided, when a tensile force or the like is applied to the steel fiber in concrete, this protruding portion resists bearing pressure against the concrete matrix.
The concrete adhesion strength increases or decreases depending on the degree of this resistance. In the present invention, in order to improve the dispersibility of the steel fibers in concrete, the length is shortened and the aspect ratio l/d is reduced, so the deformation processing of the steel fibers is as follows:
The cross-sectional area is hardly changed by bending the ends of the steel fiber or trapezoidally shaping the steel fiber, rather than just partially deforming the circular cross-section of the steel fiber as in JP-A No. 60-195044. However, from the original circular cross section, an overhang with noticeable irregularities is formed, effectively improving concrete adhesion. By increasing the overhang and improving concrete adhesion, l/
To obtain a good concrete reinforcement effect even when d is made small. Hereinafter, the steel fiber for reinforcing concrete of the present invention will be explained in detail by way of examples with reference to the attached drawings. FIG. 1 is a perspective view of one example of the steel fiber of the present invention, in which bent portions are provided at both ends of the steel fiber obtained by the wire drawing cutting method. Figure 2 a, b and c are respectively Figure 1 a-a.
FIG. Deformed portions 2 are formed alternately at pitches p on a base portion 1 having a circular cross section with a diameter d, and bent portions 3 having a length l ₁ are formed at the ends. l is the total length. In each figure in FIG. 2, the overhanging portions having areas S ₁ and S ₂ , S ₀ and S ₂ projected in the longitudinal direction from the cross section of the cross-section are indicated by the same reference numerals. The sum b of the overhang areas of S ₁ , S ₂ and S ₀ is b = S ₁ + S ₂
+S ₀ , the sum b ₁ of the overhanging area at all pitches over the entire length of the straight section of the steel fiber is b ₁ =b×l/p. The overhang area b ₂ of the bent portion 3 is approximately given by b ₂ = d×l ₁ , and the total overhang area B over the entire length of the steel fiber is B
=b ₁ +b ₂ . Regarding the steel fibers shown in FIG. 1, a steel fiber dispersibility test and a bending test on concrete specimens were conducted in the production of steel fiber reinforced concrete. The test conditions and circumstances are shown below, and the results for the steel fibers shown in Figure 1 are shown in Table 1. <Dispersibility test> The concrete mix is a base concrete with a water-cement ratio of 50%, a fine aggregate ratio of 51%, and a slump of 8 cm, mixed in a pan-type mixer with a capacity of 100, and 8 kg of steel fibers equivalent to a volume ratio of 1%. was added all at once to produce steel fiber reinforced concrete. In this case, the feeding speed of the steel fiber is 8
Kg was added all at once by hand, and the injection was completed in just 2 to 3 seconds. This is when using a disperser
It takes 12 to 13 seconds, which significantly shortens the loading time. <Bending test of concrete specimen> A bending specimen with a cross-sectional dimension of 10 cm x 10 cm and a length of 40 cm was made from the fresh concrete containing steel fiber obtained in the dispersion test, and after curing, a bending test was conducted. The specimen is divided into three equal parts and loaded at two points as shown in Figure 3 A, and the deflection is measured at the center of the fulcrum.
Determine the deflection curve, and determine the area TbKg-mm surrounded by the load-deflection curve until the amount δ ₀ in the process from the peak value of the load to fracture indicates 1/150 of the distance between the supporting points of the specimen. This was defined as the bending absorbed energy Kg-mm, and was taken as the reinforcing effect due to the addition of steel fibers. <Test results>

[Table] As is clear from Table 1, when the dispersion status of steel fibers was visually confirmed, the dispersion status of the steel fibers was very good for sample codes I to I, but the dispersion status of steel fibers for sample codes C to N was very good. The aspect ratio l/d is 50 to 58, and the total overhang area B
Even though the diameter was 8.32A to 10.44A, which met the requirements of the present invention, fiber balls were observed. This is because even if the above-mentioned aspect ratio l/d and total overhang area B are satisfied, if the processing degree (flatness) of the irregularly shaped part, that is, the overhang area b ₁ of the irregularly shaped part becomes excessive, this will cause entanglement. According to the experimental results, the overhang area _b1 needs to be suppressed to 1.95A or less, thereby avoiding the occurrence of fiber balls. There was found. Regarding the concrete reinforcement effect of the sample steel fiber, the bending absorption energy Kg-mm of the bending test mentioned above
and the total overhang area of the irregularly shaped overhang of the test steel fiber Bmm ²
Figure 6 shows the relationship between the two. Sample symbols are also included in the figure. From now on, l/d of steel fiber is 30
~60, the total overhang area B is 3A
~12A (A is the cross-sectional area of the base), a value of 70% or more of the bending absorption energy can be obtained, and it can be seen that the reinforcing effect is equivalent to that of the conventional technology with l/d of 60 to 100. . Further, the relationship between the total overhang area B of the test samples and the aspect ratio l/d is summarized and shown in FIG. 5 for the results shown in Table 1. The sample symbol is written in the figure, and the curve x for the bending absorption energy of reinforced concrete of 70% or more and the curve y for the empirically obtained dispersion performance are shown, and the good range of each is shown by hatching. . These two curves x, y
The range surrounded by, that is, the aspect ratio l/d=
25 to 57, the range of total overhang area B = 3A to 12A is,
Steel fiber reinforced concrete can be rapidly produced without using a disperser, and the concrete has good bending properties. Considering the variation in experimental results, etc., set l/d to 30~
Set to 60. Even if the aspect ratio of the steel fiber is within the above range,
The total overhang area B is outside the range of 3A to 12A above,
If it is less than 3A, the adhesion force between the steel fiber and concrete will decrease and no reinforcing effect can be expected.In order to obtain the same reinforcing effect as 3A or more, it is necessary to increase the amount of steel fiber mixed. , steel fiber reinforced concrete becomes expensive. Furthermore, if the total overhang area B is 12A or more, the depth of deformation processing becomes excessive and the tensile strength of the steel fiber decreases. For this reason, the tensile resistance force of the steel fibers in the concrete will be lower than the bearing pressure resistance force of the overhanging portion, resulting in an imbalance between the two, and in this case as well, the reinforcing effect of the steel fibers will be impaired. The steel fiber of the present invention improves its adhesion to concrete and improves its bending properties through deformation obtained by wire drawing and cutting, and by making the aspect ratio smaller than 57, the degree of deformation can be improved. Increase the total overhang area by raising the height or bending the ends. In the above-mentioned embodiment, both ends of the steel fiber were formed with bent parts, but it is also possible to form a bent part at one end. (Effect of the invention) According to the steel fiber for concrete reinforcement of the present invention,
To improve the dispersibility of steel fibers without reducing their concrete reinforcing effect, eliminate the need for special use of a dispersion machine, and thereby shorten the mixing time of steel fiber-reinforced concrete and reduce concrete placement costs. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of one example of the concrete of the present invention, FIG. 2 a is a sectional view taken along line a-a in FIG. Figure 2c
Figure 1 is a cross-sectional view taken along the line c-c in Figure 1, Figure 3 A is a side view showing the load state of the concrete specimen in the bending test, and Figure 3 B is a graph with the deflection at the center of the fulcrum on the horizontal axis and the load on the vertical axis. Figure 4 shows the bending absorption energy Kg-mm of the bending test.
Figure 5 shows the relationship between the two with mm as the vertical axis and the total overhang area as the horizontal axis. Figure 5 shows the good range of absorbed energy and dispersion performance with the vertical axis as the total overhang area and the horizontal axis as the aspect ratio. It is a diagram. 1... Base part, 2, 4, 5... Irregularly shaped part, d...
Diameter, p...pitch, _l1 ...bending section, l...total length, _S0 , _S1 , _S2 , _b2 ...projection or its area,
x, y...curve.

Claims (1)

[Claims] 1 Form unprocessed parts and processed irregularly shaped parts alternately at the required pitch on the base part with a circular cross section, and at least one end is bent to form a bent part, and the total length/diameter in the longitudinal direction is determined. The aspect ratio is in the range of 30 to 60, and the sum B of the longitudinal projected overhang area caused by processing the irregularly shaped part and forming the bent part is 3A with respect to the cross sectional area A of the base part.
1. A steel fiber for reinforcing concrete, which is in the range of ≦B≦12A, of which the longitudinal projected overhang area caused by processing the irregularly shaped portion is smaller than 1.95A.