JP2008037750A - Steel fiber for reinforcing high strength composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel fiber giving remarkably high bending strength or tensile strength to a high strength composition when the steel fiber is mixed with the high strength composition. <P>SOLUTION: The steel fiber for reinforcing the high strength composition has 0.05-0.5 mm fiber diameter, aspect ratio (fiber length/fiber diameter) of 30-150 as the fiber length, has a spiral shape having no projecting part or recessed part being ≥0.1 times the fiber diameter on the surface, the amplitude of the spiral shape being 0.3-3 times fiber length, the period of the spiral shape being 0.1-0.5 time the fiber length and has ≥150 GPs Young's modulus and ≥1 GPa tensile strength. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steel fiber that is mixed with high-strength concrete or mortar and reinforces it. More specifically, the present invention relates to steel fibers that reinforce high-strength concrete having a compressive strength of 150 MPa or higher and high-strength mortar.

  For the purpose of increasing the strength against bending and tensile of concrete and the tenacity against these, fiber reinforced concrete in which fibers are mixed into concrete is known. As this reinforcing fiber, a fiber obtained by cutting a fiber such as steel, synthetic resin or glass is generally used. In this case, in order to increase the strength against cracks in concrete, it is effective that the Young's modulus of the reinforcing fiber is larger than the Young's modulus of the concrete matrix. Therefore, as the reinforcing fiber, carbon fiber or steel fiber having a large Young's modulus is used. Glass fiber, etc. are suitable. Among these fibers, steel fibers are relatively inexpensive and are being put into practical use as reinforcing fibers for ordinary strength concrete.

  The effect of reinforcing concrete by fibers is greatly influenced by the bond strength between the fibers and the concrete matrix. When steel fibers are used as reinforcing fibers, the bond strength is smaller than the tensile strength of the fibers. Therefore, indentation with the fiber cross section deformed at regular intervals, or the entire fiber or the ends are bent to improve the bond strength. Ingenuity has been made in the past, such as creating a different shape.

  However, high-strength concrete or mortar, for example, concrete or mortar having a compressive strength of 150 MPa or more, has a problem that a sufficient reinforcing effect cannot be obtained when existing steel fibers are used. That is, when the fluidity of the uncured high-strength composition matrix is high, existing steel fibers generally have a large fiber diameter and a relatively long fiber length, so that the steel fibers tend to settle in the matrix. In addition, when the fiber is subjected to a large bending process, the fibers are entangled with each other during kneading, so that it is difficult to uniformly disperse in the matrix. In addition, the hardened high-strength composition has a solid and solid matrix, and steel fibers that have been subjected to conventional indentation and bending work are prevented from slipping at the interface between the fiber surface and the matrix when a large load is applied. In addition, there are problems such as breakage of steel fibers. Thus, since the high-strength composition which mix | blended the existing steel fiber is not enough in the reinforcement effect of a fiber, bending strength and tensile strength do not necessarily improve drastically.

Conventionally, the reinforcing materials described in the following Patent Documents 1 to 5 are known, but the reinforcing fiber of Patent Document 1 is corrugated and is different from the spiral fiber. Patent Document 2 describes a helical reinforcing fiber, but this helical shape is greatly different from the present invention in fiber diameter and helical amplitude. Patent Document 3 exemplifies a helical metal facet as a reinforcing material, but is not a helical shape. The reinforcing fiber of Patent Document 4 is corrugated and is different from a spiral fiber. Patent Document 5 describes a stainless steel fiber as a reinforcing fiber, but it is not helical. Therefore, none of the reinforcing materials described in Patent Documents 1 to 5 can obtain the effect of the present invention.
Japanese Patent Publication No. 04-04347 Japanese Patent Laid-Open No. 01-122942 JP 52-033919 A Japanese Patent Laid-Open No. 07-053247 Japanese Unexamined Patent Publication No. Sho 63-29559

  The present invention solves such conventional problems for reinforcing fibers used in high-strength compositions, and when blended in high-strength compositions, it provides dramatically higher bending strength and tensile strength. It provides a steel fiber that can be used.

  In the present invention, the fiber diameter is 0.05 mm to 0.5 mm, the fiber length is 30 to 150 in terms of the fiber aspect ratio (fiber length / fiber diameter), and the surface has protrusions or more than 0.1 times the fiber diameter. The spiral shape has no depression, the amplitude of the spiral shape is 0.3 to 3 times the fiber diameter, the period of the spiral shape is 0.1 to 0.5 times the fiber length, and the Young's modulus is 150 GPa As described above, the steel fiber for reinforcing a high strength composition having a tensile strength of 1 GPa or more.

  The reinforcing steel fiber of the present invention exhibits an excellent reinforcing effect for high-strength compositions such as high-strength concrete. In addition to the high compressive strength of the composition, dramatically higher bending strength and tensile strength are achieved. Strength can be imparted.

Hereinafter, the present invention will be described in detail according to embodiments.
When reinforcing short fibers with concrete to reinforce the strength against bending and tension, the shape and amount of reinforcing fibers mixed in, the mechanical properties such as Young's modulus and tensile strength of the reinforcing fibers, and the mechanical properties of the matrix Of course, it is important to control the interface properties such as the adhesion strength between the reinforcing fiber and the matrix.

  This is because the reinforcing fiber bears a load even when the matrix is not cracked, and the proportion of the burden is governed by the ratio of the Young's modulus between the matrix and the reinforcing fiber. At this time, the limit of the load burden of the reinforcing fiber is determined in relation to the strength of the reinforcing fiber and the adhesion strength between the reinforcing fiber and the matrix. That is, if the strength of the reinforcing fiber is smaller than the adhesive strength, the reinforcing fiber is broken, and if the adhesive strength is low, the interface between the reinforcing fiber and the matrix is peeled off or slipped. It is because the load burden of the reinforcing fiber is reduced.

  On the other hand, when cracks occur in the matrix, the load is only borne by the fibers bridging the cracks. Similarly, the reinforcement fibers are related to the fiber strength and the adhesion strength to the matrix. The limit of load sharing is determined.

  Therefore, in order to reinforce a high-strength composition with high fluidity such as concrete and mortar, and to obtain dramatically high bending strength and tensile strength in addition to its high compressive strength, it is a machine that matches well with the mechanical properties of the matrix. It is indispensable to select a reinforcing fiber having a specific characteristic and to optimize an interface characteristic between the reinforcing fiber and the matrix.

  For this purpose, steel fibers made of carbon steel or stainless steel are suitable as reinforcing fibers. The Young's modulus of the steel fiber is desirably 150 GPa or more. The tensile strength of the steel fiber is preferably 1 GPa or more, and more preferably 1.5 GPa or more. If the Young's modulus of the steel fiber is less than 150 GPa, it approaches the Young's modulus of the concrete matrix, so that the load sharing of the fiber is reduced and the crack load of the high-strength composition cannot be increased.

  The diameter of the steel fiber is desirably 0.05 mm to 0.5 mm. If the diameter is less than 0.05 mm, the fibers tend to be clumped due to interference between the fibers during kneading. On the other hand, if the diameter of the steel fiber is larger than 0.5 mm, the fiber tends to settle before the high-strength composition is cured. For this reason, since the dispersion | distribution of the steel fiber mix | blended in the high intensity | strength composition is not uniform in any case, sufficient reinforcement effect is not acquired.

  The length of the steel fiber is preferably 30 to 200 in aspect ratio (fiber length / fiber diameter). In addition, if the aspect ratio is 50 to 150, the fluidity at the time of kneading is hardly lowered, the amount of mixed fibers can be made relatively large, and as a result, a sufficient reinforcing effect can be obtained, which is further desirable. On the other hand, when the aspect ratio of the steel fiber is less than 30, it is not desirable because the steel fiber bridging the cracked portion is easily pulled out when the crack opening is widened, and the reinforcing effect of the fiber is lowered. Further, if the aspect ratio of the steel fiber exceeds 200, the fluidity is lowered at the time of kneading, so that not only the workability such as pouring into a mold is inferior but also the bubbles are difficult to escape. Incidentally, if the amount of mixed fibers is reduced, the decrease in fluidity can be suppressed, but the load of the fibers is reduced because the amount of fibers is small, and the strength of the high-strength composition reinforced with fibers is also undesirable.

  It is desirable that the surface of the steel fiber is smooth without protrusions or depressions that are 0.1 times or more the fiber diameter. If there are no protrusions or depressions greater than 0.1 times the fiber diameter, the relative movement between the steel fibers and the matrix will continue even after the interface between the steel fibers bridging the cracks in the concrete and the concrete matrix peels. Since it is not restrained, the steel fiber is difficult to break, and the high-strength composition can be made tough. On the other hand, if there are protrusions or depressions that exceed 0.1 times the fiber diameter, the peak value of the adhesion strength between the steel fibers and the matrix will increase, but the slippage between the steel fibers and the matrix will be suppressed, so the fiber will break. As a result, the adhesion of the steel fibers bridging the cracked portion immediately decreases when a crack occurs in the concrete. As a result, brittle fracture of the high strength composition occurs.

  The steel fiber of the present invention has a spiral shape. In the case of the spiral shape, even when the interface between the steel fiber and the matrix bridging the crack is peeled off, an appropriate frictional force is applied to the interface between the steel fiber and the matrix during the relative movement of the steel fiber and the matrix. As a result, the toughness of the fiber-reinforced high strength composition can be increased.

  In the helical steel fiber according to the present invention, the amplitude of the spiral is desirably 0.3 to 3 times the fiber diameter. If the amplitude of the helix is less than 0.3 times the fiber diameter, the frictional force generated during the relative movement between the fiber and the matrix is small, which is not preferable. On the other hand, if the amplitude exceeds three times the fiber diameter, the fibers are entangled during kneading of the high-strength composition, so that it is difficult to uniformly disperse the fibers.

  Moreover, about the helical steel fiber which concerns on this invention, it is desirable for the period of a spiral to be 0.1 to 0.5 time of fiber length. When this period exceeds 0.5 times the fiber length, sufficient drag does not act on the fiber during relative movement of the fiber and the matrix, and the frictional force generated at the interface between the fiber and the matrix decreases rapidly. Further, if this period is less than 0.1 times the fiber length, the frictional force becomes too large and the relative movement between the fiber and the matrix is restricted. As a result of these, a sufficient reinforcing effect by the steel fibers cannot be obtained, and the high-strength composition reinforced with fibers becomes brittle fracture, which is undesirable. In addition, the amplitude or period of the spiral is based on the fiber center.

  Hereinafter, the present invention will be specifically described by way of examples. The present invention is not limited to these examples.

[Example 1]
As raw materials for the high-strength composition (high-strength concrete) serving as a matrix, 2246 g of medium heat cement, 250 g of silica fume, 1880 g of sand (silica sand produced in Yamagata Prefecture: No. 4), and admixture (polycarboxylic acid-based high-performance water reducing agent 62 450 g of water containing 0.4 g and defoaming agent 0.6 g) was weighed. Steel fibers were also prepared. This steel fiber has a diameter of 0.05 mm, an aspect ratio of 120 (length: 6 mm), and surface roughness as evaluated by a microscope is 0.005 mm, and the spiral shape has an amplitude of 0.1 mm (twice the fiber diameter). ) And a period of 2.4 mm (0.4 times the fiber length), and the tensile strength and Young's modulus of the fiber are 2 GPa and 200 GPa, respectively. 316 g of this fiber was weighed. In addition, the fiber mixing rate with respect to this concrete is 2 volume%.

  The weighed raw materials were kneaded using a Hobart mixer. A sample in which water, cement and silica fume were mixed in advance was kneaded, and then sand and fibers were added to prepare a sample. This sample was cast into a mold having a length of 160 mm, a width of 40 mm, and a depth of 40 mm in order to produce a specimen for measuring bending strength. Further, in order to produce a specimen for measuring the tensile strength, the sample was poured into a mold having a length of 300 mm, a width of 50 mm, and a depth of 10 mm and molded. After 24 hours of this molding, the mold was removed, and then steam curing was performed at 80 ° C. for 48 hours to obtain a specimen.

  For this specimen, the bending strength was measured by performing a three-point bending test using an Instron type tester with a distance between the lower fulcrums of 120 mm, and calculating from the maximum value of the load. Tensile strength is measured by fixing an aluminum plate (50mm square, 1.5mm thickness) to both ends of the body with epoxy resin, and then performing a uniaxial tensile test using an Instron type testing machine. The tensile strength was calculated from the value. In any test, the test speed was a crosshead speed of 0.5 mm / min.

  The flow value for evaluating the fluidity of the sample immediately after kneading is to pour the sample into a JIS mortar ring placed on a horizontal 350 mm square glass plate, scrape the top of the ring, gently lift the ring, The major axis when the sample was stationary and the diameter orthogonal thereto were measured, and the average value of the two was taken as the flow value. As a result, the flow value was as good as 230 mm, the three-point bending strength was 50 MPa, and the uniaxial tensile strength was 20 MPa.

[Example 2]
The steel fiber used is a spiral fiber with a diameter of 0.5 mm and an aspect ratio of 50 (length 25 mm). The amplitude of the helix is 1 mm (twice the diameter), the spiral period is 5 mm (0.2 times the length), The flow value, three-point bending strength and uniaxial tensile strength were measured in the same manner as in Example 1 except that the mixing amount of fibers was 554 g (fiber mixing rate: 3.5% by volume) and the mixing amount of sand was 1802 g. As a result, the flow value was 250 mm, the three-point bending strength was 45 MPa, and the uniaxial tensile strength was 20 MPa, all showing good values.

[Reference Example 1]
The steel fiber used is a corrugated fiber with a diameter of 0.1 mm and an aspect ratio of 200 (length 20 mm), a corrugated amplitude of 0.2 mm (twice the diameter), and a corrugated period of 6 mm (0.3 times the length). The flow value, the three-point bending strength, and the uniaxial tensile strength were measured in the same manner as in Example 1 except that the fiber mixing amount was 158 g (fiber mixing rate: 1 vol%) and the sand mixing amount was 1935 g. As a result, the flow value was 240 mm, the three-point bending strength was 45 MPa, and the uniaxial tensile strength was 20 MPa, all showing good values.

Example 3
The steel fiber used is a spiral fiber having a diameter of 0.3 mm and an aspect ratio of 30 (length: 9 mm), a spiral amplitude of 0.6 mm (twice the diameter), and a spiral period of 1.8 mm (length of 0.5 mm). 2 times), the flow value, the three-point bending strength and the uniaxial tensile strength were measured in the same manner as in Example 1 except that the fiber mixing amount was 1264 g (fiber mixing rate: 8 vol%) and the sand mixing amount was 1564 g. . As a result, the flow value was 230 mm, the three-point bending strength was 42 MPa, and the uniaxial tensile strength was 18 MPa, all showing good values.

[Reference Example 2]
The steel fiber used is a corrugated fiber with a diameter of 0.4 mm and an aspect ratio of 50 (length 20 mm). The corrugation amplitude is 0.4 mm (one time the diameter), and the corrugation period is 5 mm (the length is 0.25 times). The flow value, the three-point bending strength and uniaxiality were the same as in Example 1 except that the fiber surface irregularity was 0.04 mm, the fiber mixing amount was 790 g (fiber mixing rate 5 vol%), and the sand mixing amount 1722 g. Tensile strength was measured. As a result, the flow value was 235 mm, the three-point bending strength was 40 MPa, and the uniaxial tensile strength was 18 MPa, all showing good values.

Example 4
The steel fiber used is a spiral fiber having a diameter of 0.1 mm and an aspect ratio of 150 (length 15 mm), a spiral amplitude of 0.03 mm (0.3 times the diameter), and a spiral period of 3 mm (length of 0.0 mm). The flow value, three-point bending strength, and uniaxial tensile strength were measured in the same manner as in Example 1 except that it was 2 times. As a result, the flow value was 230 mm, the three-point bending strength was 45 MPa, and the uniaxial tensile strength was 17 MPa, all showing good values.

Example 5
The steel fiber used is a spiral fiber having a diameter of 0.3 mm and an aspect ratio of 40 (length 12 mm), a spiral amplitude of 0.9 mm (three times the diameter), and a spiral period of 1.8 mm (length of 0.8 mm). 15 times), the flow value, the three-point bending strength, and the uniaxial tensile strength were measured in the same manner as in Example 1 except that the fiber mixing amount was 790 g (fiber mixing rate: 5% by volume) and the sand mixing amount was 1722 g. . As a result, the flow value was 230 mm, the three-point bending strength was 41 MPa, and the uniaxial tensile strength was 19 MPa, all showing good values.

Example 6
The steel fiber used is a spiral fiber with a diameter of 0.1 mm and an aspect ratio of 80 (length 8 mm), a spiral amplitude of 0.1 mm (1 time of the diameter), and a spiral period of 0.8 mm (0.1 times the length). ), The surface roughness of the fiber is 0.01 mm, the mixing amount of the fiber is 554 g (fiber mixing ratio: 3.5% by volume), and the mixing amount of sand is 1802 g. Uniaxial tensile strength was measured. As a result, the flow value was 240 mm, the three-point bending strength was 58 MPa, and the uniaxial tensile strength was 23 MPa, all showing good values.

Example 7
The steel fiber used is a spiral fiber with a diameter of 0.2 mm and an aspect ratio of 80 (length 16 mm), a spiral amplitude of 0.2 mm (1 times the diameter), and a spiral period of 8 mm (0.5 times the length). ), The surface roughness of the fiber is 0.01 mm, the mixing amount of the fiber is 554 g (fiber mixing ratio: 3.5% by volume), and the mixing amount of sand is 1802 g. Uniaxial tensile strength was measured. As a result, the flow value was 250 mm, the three-point bending strength was 45 MPa, and the uniaxial tensile strength was 20 MPa, all showing good values.

[Comparative Example 1]
The steel fiber used was a spiral fiber with a diameter of 0.02 mm, the amplitude of the spiral was 0.04 mm (twice the diameter), the spiral period was 0.96 mm (0.4 times the length), and the surface irregularities were zero. The flow value, three-point bending strength and uniaxial tensile strength were measured in the same manner as in Example 1 except that the thickness was 0.002 mm. As a result, since the fiber was too thin, it showed a brittle fracture as compared with Example 1, the three-point bending strength was inferior to 16 MPa, the uniaxial tensile strength was inferior to 7.2 MPa, and the flow value was 180 mm, which was low in fluidity. It was.

[Comparative Example 2]
The steel fiber used was a spiral fiber having a diameter of 0.6 mm, and the example 2 was different from that of Example 2 except that the amplitude of the helix was 1.2 mm (twice the diameter) and the period of the helix was 6 mm (0.2 times the length). Similarly, the flow value, three-point bending strength and uniaxial tensile strength were measured. As a result, the flow value was 240 mm and the fluidity did not decrease, but the fiber was too thick, so it showed a brittle fracture compared to Example 2, the three-point bending strength was 21 MPa, and the uniaxial tensile strength was It was inferior to 8.3 MPa.

[Comparative Example 3]
The flow value and three-point bending strength were the same as in Reference Example 1 except that the used fiber had an aspect ratio of 240 (length 24 mm), and the waveform period was 7.2 mm (0.3 times the length). And the uniaxial tensile strength was measured. As a result, since the fiber was too long, the flow value became 170 mm, the fluidity was lowered, and the workability at the time of molding was inferior. Further, the three-point bending strength was 20 MPa and the uniaxial tensile strength was 9.3 MPa, which was inferior to Example 3.

[Comparative Example 4]
The flow value and three points were the same as in Example 3 except that the used fiber had an aspect ratio of 20 (length: 6 mm) and a spiral period of 1.2 mm (0.2 times the length). Bending strength and uniaxial tensile strength were measured. As a result, the flow value was 235 mm, and the fluidity was not lowered, but the test piece exhibited a brittle fracture because the fiber was too short. The three-point bending strength of this specimen was 22 MPa, and the uniaxial tensile strength was 8.5 MPa, which was inferior to Example 4.

[Comparative Example 5]
The flow value, three-point bending strength, and uniaxial tensile strength were measured in the same manner as in Reference Example 2 except that the fiber used was indented with a surface irregularity of 0.1 mm. As a result, since the entanglement between the fibers was remarkable, the flow value was 200 mm, and the fluidity was lowered. In addition, during the strength test, the specimen showed a brittle fracture because the matrix had a tendency to break when the fiber pulled out. This sample had a three-point bending strength of 22 MPa and a uniaxial tensile strength of 8.8 MPa, which was inferior to Example 5.

[Comparative Example 6]
The flow value, the three-point bending strength, and the uniaxial tensile strength were measured in the same manner as in Example 4 except that the fibers used were linear without spirals or corrugations. As a result, the flow value was 220 mm, and the fluidity of the sample after kneading did not decrease. However, in the strength test, the three-point bending strength was 21 MPa and the uniaxial tensile strength was 9 because the fiber adhesion strength was insufficient. 0.1 MPa, which is lower than that of Example 6.

[Comparative Example 7]
The flow value, three-point bending strength and uniaxial tensile strength were measured in the same manner as in Example 5 except that the used fiber had a helical amplitude of 1.2 mm (4 times the diameter). As a result, since the entanglement between the fibers was remarkable, the flow value was 170 mm, and the decrease in fluidity was remarkable. Further, during the strength test, since the matrix tends to break when the fibers are pulled out, the strength of the specimen is low and brittle fracture is shown. The strength measurement results were a three-point bending strength of 20 MPa and a uniaxial tensile strength of 8.4 MPa, which was inferior to Example 7.

[Comparative Example 8]
The flow value, three-point bending strength, and uniaxial tensile strength were measured in the same manner as in Example 6 except that the used fiber had a helical period of 0.64 mm (0.08 times the length). As a result, since the entanglement between the fibers was remarkable, the kneading operation was somewhat difficult, and the flow value was 170 mm, and the decrease in fluidity was remarkable. Further, in the strength test, the strength of the specimen was low because of the tendency to break the matrix when the fiber was pulled out, and the brittle fracture was shown. The strength measurement results were a three-point bending strength of 16 MPa and a uniaxial tensile strength of 6.9 MPa, which were inferior to those of Example 8.

[Comparative Example 9]
The flow value, three-point bending strength, and uniaxial tensile strength were measured in the same manner as in Example 7 except that the used fiber had a spiral period of 9.6 mm (0.6 times the length). As a result, the flow value is 250 mm, and the fluidity of the sample does not decrease. However, in the strength test, the three-point bending strength is 21 MPa and the uniaxial tensile strength is 8.7 MPa because the fiber adhesion strength is insufficient. Low compared to 9.

  The results of Examples 1 to 7, Reference Examples 1 and 2, and Comparative Examples 1 to 9 are shown in Table 1.

Claims (1)

  The fiber diameter is 0.05 mm to 0.5 mm, the fiber length is 30 to 150 in terms of the fiber aspect ratio (fiber length / fiber diameter), and the surface has no protrusions or depressions greater than 0.1 times the fiber diameter. It has a spiral shape, the amplitude of the spiral shape is 0.3 to 3 times the fiber diameter, the period of the spiral shape is 0.1 to 0.5 times the fiber length, Young's modulus 150 GPa or more, tensile strength A steel fiber for reinforcing a high-strength composition characterized by being 1 GPa or more.