KR20130129386A - Steel fibre for reinforcing concrete or mortar provided with flattened sections - Google Patents

Abstract

The present invention relates to steel fibers for reinforcing concrete or mortar. The steel fiber includes an intermediate part having a predetermined length L, a first fixing end provided at one end of the intermediate part, and a second fixing end provided at the other end of the intermediate part. The middle portion includes a first flattening section, a second flattening section and a central section. The central section is located between the first flattened section and the second flattened section. The first flattened section is located close to but not immediately adjacent to the first anchoring end and the second flattened section is located close to but not immediately adjacent to the second anchoring end. The middle part has a tensile strength (R _m ) of at least 1000 MPa and an elongation (A _{g + e} ) at maximum load of at least 2.5%. The invention also relates to the use of steel fibers for concrete structures comprising the steel fibers according to the invention and for load bearing structures of concrete.

Description

STEEL FIBRE FOR REINFORCING CONCRETE OR MORTAR PROVIDED WITH FLATTENED SECTIONS}

The present invention relates to a steel fiber for reinforcing concrete or mortar, wherein the steel fiber has an intermediate portion and at least one fixing end, and at least one flattening section is provided in the intermediate portion. Steel fiber according to the present invention exhibits excellent performance in the service-ability limit state (SLS) and ultimate limit state (ULS) when embedded in concrete or mortar. The present invention also relates to concrete or mortar structures comprising such steel fibers.

Concrete is a brittle material with low tensile strength and low drawing ability. Fiber reinforced concrete, more specifically metallic fiber reinforced concrete, has been developed to improve the properties of concrete such as tensile strength and softening ability. It is known in the art that fiber properties such as fiber concentration, fiber geometry and fiber aspect ratio significantly affect the performance of reinforcement concrete.

For fiber geometries, it is known that fibers having a shape different from the straight shape provide better fiber fixation in concrete or mortar. It is also known that fibers which do not show a tendency to form balls when added or mixed with concrete or mortar are preferred. Various examples of different fiber geometries are known in the art. For example, there are fibers that are wavy over all or some length. Examples of steel fibers corrugated over their entire length are described in WO84 / 02732. Fibers with hook shaped ends are also known in the art. Such fibers are described, for example, in US 3,942,955. Likewise, there are fibers in which the cross-sectional profile varies over length, such as fibers provided with thickness extension sections and / or planarization sections. An example of a steel fiber provided with a thickness expansion section is a steel fiber having a nail head-shaped thickness extension at each end as described in US 4,883,713. Japanese Patent 6-294017 describes flattening steel fibers over their entire length. German utility model G9207598 describes flattening only the middle part of a steel fiber having a hook-shaped end. US 4,233,364 describes straight steel fibers having flattened ends with ends provided with flanges on a plane substantially perpendicular to the flattened ends. Steel fibers with hook shaped flattened ends are known from EP 851957 and EP 1282751.

Currently known prior art concrete reinforcing fibers perform very well in known applications such as industrial flooring, sprayed concrete, paving and the like. However, a drawback of the currently known prior art fibers is that their performance in extreme limit states (ULS) is relatively low when the fibers are used in small or medium doses. For heavier structural applications, such as beams and expensive slabs, high dosages typically range from 0.5 vol% (40 kg / m3) to 1.5 vol% (120 kg / m3) to provide the necessary ULS performance. do. If the input amount is large, the mixing and pouring of steel fiber reinforced concrete is not easy. Some prior art fibers fail at ULS because they break at a lower crack opening displacement (CMOD) than is required for ULS. Other fibers, such as fibers with hook-shaped ends, are configured to draw and do not function properly in ULS.

An object of the present invention is to provide a steel fiber for reinforcing concrete or mortar that avoids the disadvantages of the prior art.

Another object of the present invention is a greater than 0.5 mm, greater than 1 mm, greater than 1.5 mm or greater than 2 mm during the three point bending test according to European standard EN 14651 (June 2005). It is to provide a steel fiber capable of bridging crack opening displacements that are larger, greater than 2.5 mm or even greater than 3 mm.

It is another object of the present invention to provide steel fibers which exhibit good anchorage in concrete or mortar.

Another object of the present invention is to provide a steel fiber which does not exhibit a tendency to form balls when mixed with concrete or mortar.

Another object of the present invention is to provide a steel fiber which can be advantageously used in structural applications, in which steel fibers are used in small or medium doses, typically in a dose of 1 vol% or 0.5 vol%.

It is yet another object of the present invention to provide steel fibers which enable to reduce or prevent the creep behavior of crack generating concrete reinforced with these fibers in the tensile zone.

According to a first aspect of the present invention, there is provided a steel fiber for reinforcing concrete or mortar. The steel fiber includes an intermediate portion, a first fixing end provided at one end of the intermediate portion, and a second fixing end provided at the other end of the intermediate portion. The intermediate portion has a predetermined length L. The middle portion includes a first flattening section, a second flattening section and a central section. The first flattening section has a length l _fl1 . The second planarization section has a length l _fl2 . The central section of the middle portion has a length l '. The central section is located between the first flattened section and the second flattened section. The first flattening section is located close to but not immediately adjacent to the first anchoring end, and the second flattening section is located close to but not immediately adjacent to the second anchoring end. The central section has a tensile strength (R _m ) of at least 1000 MPa and an elongation (A _{g + e} ) at maximum load of at least 2.5%.

Preferably, the central section of the middle section, ie the section of the middle section located between the first and second flattening sections, comprises a substantial portion of the middle section. Preferably, the ratio (= ratio l '/ L) of the length l' of the central section divided by the length L of the middle portion is greater than 0.50. More preferably, the ratio l '/ L is greater than 0.55, greater than 0.60, greater than 0.65, greater than 0.70 or even greater than 0.75. The length l 'is preferably between 10 mm and 40 mm, more preferably between 25 mm and 40 mm.

The expression “close to but not immediately adjacent to the anchoring end” means that the distance between the anchoring end and the flattening section is short but not zero. Preferably, the distance between the first anchoring end and the first flattening section and / or the distance between the second anchoring end and the second flattening section is between 0.5 mm and 20 mm, such as between 1 mm and 5 mm, such as 2 mm or 3 mm. to be.

Since the first flattened section is located close to but not immediately adjacent to the first anchoring end, the intermediate portion has a section located between the first anchoring end and the first flattening section. Similarly, since the second flattened section is located close to but not immediately adjacent to the second flattened section, the intermediate portion has a section located between the second flattened section and the second anchoring end.

Therefore, the middle portion of the steel fiber according to the present invention,

A section between the first anchoring end and the first flattening section,

A first planarization section,

-The central section,

A second planarization section,

Successively including a section between the second planarization section and the second anchoring end.

The middle portion is preferably straight or straight. When the middle part is straight, the section between the first anchoring end and the first flattening section, the first flattening section, the central section, the second flattening section and the section between the second flattening section and the second fixing end are all in one straight line. Is placed on.

The central section of the middle part is straight or straight.

The length L of the middle part is defined as the total length of the middle part, so that the length between the first anchoring end and the first flattening section, the length of the first flattening section l _fl1 , the length of the central section l ', 2 corresponds to the sum of the length l _{fl2 of the} flattened section and the length between the second flattened section and the second anchoring end.

In the middle of the steel fiber according to the invention it is provided that there is provided a centralized section (preferably an unflattened section) of considerable length (l ') located between the two flattened sections as well as two flattened sections having a limited length. It is essential to. The central section has a tensile strength (R _m ) of at least 1000 MPa and an elongation (A _{g + e} ) at maximum load of at least 2.5%. The steel fiber according to the present invention shows excellent performance in both the use limit state (SLS) and the limit limit state (ULS) of concrete or mortar.

It is known in the art that providing flattening zones in steel fibers improves the anchoring force of the steel fibers in concrete or mortar. Various ways of providing planarization zones in steel fibers have been described in the prior art.

Japanese Patent 6-294017 describes a method of flattening steel fibers over their entire length.

German Utility Model 9207598 describes a method of planarizing only the middle part of a steel fiber with hook-shaped ends.

US Pat. No. 4,233,364 describes a straight steel fiber having a flattened end having an end provided with a flange on a plane substantially perpendicular to the flattened end.

German utility model 9202767 describes steel fibers with a number of flattening sections in the middle.

EP 851957 and EP 1282751 describe steel fibers with hook-shaped flattened ends.

The steel fibers according to the invention are distinguished from the fibers of the prior art in that two flattened sections of limited length near the anchoring end are provided in the middle of the steel fibers according to the invention. Surprisingly, it has been found that steel fibers provided with two flattened sections of limited length close to but not immediately adjacent to the anchoring end exhibit improved anchorage in concrete or mortar.

The steel fibers according to the invention have a limit of use (SLS) and limit of limit (ULS) of concrete or mortar structures when used in medium or small doses, i.e. less than 1 vol% or less than 0.5 vol%, such as 0.25 vol%. It works particularly well in both. It is known in the art that increasing the amount of fibers in concrete has a positive effect on the performance of fiber reinforced concrete. A great advantage of the present invention is that medium to small dosages of steel fibers yield good performance in SLS and ULS. In the present invention, the material properties used to evaluate the performance in ULS and SLS of steel fiber reinforced concrete are residual bending tensile strength (f _{R , i} ). The residual bending tensile strength is derived from the load at the predetermined crack opening displacement (CMOD) or midspan deflection (δ _R ). Residual bending tensile strength is determined by a three point bending test according to European standard EN 14651 (described below in this application). Residual bending tensile strength (f _{R , 1} ) is determined at CMOD ₁ = 0.5 mm (δ _{R, 1} = 0.46 mm), and residual bending tensile strength (f _{R , 2} ) is CMOD ₂ = 1.5 mm (δ _{R, 2)} = 1.32 mm), residual bending tensile strength (f _{R , 3} ) is determined at CMOD ₃ = 2.5 mm (δ _{R, 3} = 2.17 mm), and residual bending tensile strength (f _{R , 4} ) is CMOD ₄ It is determined at = 3.5 mm (δ _{R, 1} = 3.02 mm). Residual bending tensile strength (f _{R , 1} ) is a key requirement of the SLS configuration. Residual bending tensile strength (f _{R , 3} ) is a key requirement of the ULS configuration.

Unlike the steel fibers known in the art, in the steel fibers according to the present invention, residual bending tensile strength is used even when a dose of less than 1 vol% or less than 0.5 vol%, such as a small or moderate amount of steel fiber, such as 0.25 vol%, is used. strength (f _{R, 3)} and the ratio between the residual bending tensile strength _{(f R, 1) (f} R, 3 / f R, 1) is higher. In the fibers according to the invention, when an input of less than 1 vol% or an input of less than 0.5 vol%, such as 0.25 vol%, is used, the ratio (f _{R, 3} / f _{R, 1} ) is preferably greater than 1. High, more preferably higher than 1.15, such as for example 1.2 or 1.3.

In concrete reinforced with steel fibers according to the invention using a dose of 0.5 vol%, the residual bending tensile strength (f _{R , 3} ) using C35 / 45 is higher than 3.5 MPa, preferably higher than 5 MPa, More preferably it is higher than 6 MPa, for example 7 MPa.

Fibers known in the art, such as steel fibers with conical ends (nail heads) made of low carbon steel wire, for example, function well when the width or growth is limited to about 0.5 mm (SLS). However, these fibers do not perform well in ULS. This type of steel fiber breaks at lower crack opening displacement than required for ULS. When used in medium dosages on moderate strength concrete, such as C35 / 45 concrete, the ratios f _{R , 3} / f _{R ,} 1 are lower than one. Another fiber known in the art is a fiber having a hook-shaped end as known, for example, via EP 851957, which is configured to be drawn. Even for this type of fiber, the ratio (f _{R , 3} / f _{R , 1} ) is lower than ₁ when administered in medium doses to moderate strength concrete.

The first flattened section has a predetermined length l _fl1 and the second flattened section has a predetermined length l _fl2 . The length of the first flattened section (l _fl1) and the length of the second flattened section (l _fl2) is preferably between 0.5 mm and 10 mm, more preferably between 1 mm and 3 mm, for example 2 mm or 2.5 mm . The length of the first flattened section _(fl1 l) the length of the second flattened section (l _fl2) may be the same or different. Preferably, the first is the same length (l _fl1) and length (l _fl2) of the second flattened section of the flattened section.

The length of the first flattened section _(fl1 l) the length of the second flattened section (l _fl2) is short compared to the intermediate portion of the length (L). The ratio l _fl1 / L and the ratio l _fl2 / L are preferably lower than 0.15. More preferably, the ratio l _fl1 / L and the ratio l _fl2 / L are lower than 0.10 or lower than 0.07.

The total length of the first and second flattened sections is also short compared to the length L of the middle portion. The total length of the first and second flattened sections corresponds to the sum of the length l _fl1 of the first flattened section and the length l _fl2 of the second flattened section. The ratio ((l _fl1 + l _fl2 ) / L) is preferably lower than 0.30. More preferably, the ratio ((l _fl1 + l _fl2 ) / L) is lower than 0.20 or lower than 0.14.

The first flattened section and the second flattened section preferably have a rectangular or substantially rectangular cross section. In alternative embodiments, the first and second flattened sections have an elliptical or substantially elliptical cross section.

Although a circular cross section is preferred, the central section can have any type of cross section. Preference is given to a central section having the same cross section over the entire length l 'of the central section. In some embodiments, it is essential that the central section has the same cross section over the entire length l 'of the central section. The central section can be flattened, for example rectangular, substantially rectangular, oval or substantially oval. However, if the middle portion (such as the central section) other than the flattened section or sections is flattened, the portion is flattened to a lesser extent than the flattened section or flattened sections.

Likewise, the section between the first anchoring end and the first flattening section and the section between the second anchoring end and the second flattening section can have any type of cross section, although a circular cross section is preferred. Preferably, the section between the first anchoring end and the first planarizing section and the section between the second anchoring end and the second planarizing section have the same cross section over the entire length of these sections. In some embodiments, it is essential that the sections between the first anchoring end and the first flattening section and the sections between the second anchoring end and the second flattening section have the same cross section over the entire length of these sections. The section between the first anchoring end and the first flattening section and the section between the second anchoring end and the second flattening section may be flattened, for example rectangular, substantially rectangular, elliptical or substantially elliptical. However, if these sections are flattened, the sections are flattened to a lower level than the flattened section or flattened sections. Preferably, the section between the first anchoring end and the first flattening section and the section between the second anchoring end and the second flattening section have the same cross section as the central section of the middle portion.

Compared to the thickness of the central section, the thickness of the first flattened section and the second flattened section preferably decreases from 10% to 40%, such as between 15% and 30%, such as 20% or 25%. The decrease in thickness has a positive effect on the anchoring capacity of the steel fibers in the concrete or mortar and the performance of the steel fibers in the concrete or mortar. However, thickness reductions in excess of 40% are not desirable because such a decrease in thickness causes the strength of the middle portion to be highly weakened.

In some embodiments of the present invention, flattened sections having one side flattened are provided in the steel fibers. In another embodiment of the present invention, flattened sections having both sides flattened are provided in the steel fibers.

In a preferred embodiment, the flattening section comprises a section that is flattened on a plane substantially parallel to the plane of the steel fibers. In an alternative embodiment, the flattening section includes a section that is flattened on a plane substantially perpendicular to the plane of the steel fibers.

Load capacity ( F _m )-The tensile strength( R _m )

The steel fiber according to the invention, more particularly the central section of the middle part of the steel fiber according to the invention, preferably has a high maximum load capacity F _m . The maximum load capacity (F _m ) is the maximum load the steel fiber can withstand during the tensile test. Since the tensile strength (R _m ) is the maximum load capacity (F _m ) divided by the original cross section of the steel fiber, the maximum load capacity (F _m ) of the central section portion is directly related to the tensile strength (R _m ) of the central section. . In the steel fibers according to the invention, the tensile strength of the central section of the steel fibers is preferably above 1000 MPa, more preferably such as above 1500 MPa, eg above 1750 MPa, eg above 2000 MPa, eg above 2500 MPa It exceeds 1400 MPa. Due to the high tensile strength of the steel fibers according to the invention the steel fibers can withstand high loads. Thus, if the steel fibers used provide good fixation, higher tensile strength is directly reflected with less fiber input.

Elongation at Maximum Load

According to a preferred embodiment, the central section of the steel fiber according to the invention, more particularly the middle part of the steel fiber according to the invention, has an elongation (A _{g + e} ) at maximum load of at least 2.5%. According to a particular embodiment of the invention, the central section of the middle part of the steel fiber is higher than 2.75%, higher than 3.0%, higher than 3.25%, higher than 3.5%, higher than 3.75% or higher than 4.0%. , Higher than 4.25%, higher than 4.5%, higher than 4.75%, higher than 5.0%, higher than 5.25%, higher than 5.5%, higher than 5.75%, or even higher than 6.0% Elongation at load (A _{g + e} )

In the context of the present invention, elongation at break (A _{g + e} ), rather than elongation at break (A _t ), is used to characterize the elongation of the steel fiber, more particularly the central section of the middle of the steel fiber. The reason is that once the maximum load is reached, shrinkage of the soluble surface of the steel fiber begins and no higher load is absorbed. Elongation at full load (A _{g + e} ) is the sum of plastic elongation at maximum load (A _g ) and elastic elongation.

Elongation at high maximum load (A _{g + e} ) can be obtained by applying a specific stress relaxation treatment, such as heat treatment, to the steel wire that is the material of the steel fibers. In this case, at least the central section of the middle part of the steel fiber is in a stress relaxed state.

Steel fibers with high ductility or elongation at high peak load (A _{g + e} ) are preferred, such fibers exceeding 1.5 mm, exceeding 2.5 mm or 3.5 mm in a three-point bending test according to EN 14651. It is not broken in excess of CMOD.

Fixation

Preferably, the steel fibers according to the invention have a high degree of anchorage in concrete or mortar. By providing the flattening section according to the invention in the middle of the steel fiber, the fixing force of the steel fiber in concrete or mortar is significantly improved. It is known in the art that the type of anchoring end directly affects the anchoring force of the steel fibers in concrete or mortar. The fixing end may comprise a thickness expanding or expanding fixing end, a nail head, a flattening fixing end, a hook-shaped fixing end, a bent or corrugated fixing end or any combination thereof. According to the present invention, it has been surprisingly found that for most anchoring end types, the anchoring force in the concrete or mortar of steel fibers is improved by providing a flattening section near the anchoring end but not immediately adjacent to the middle of the steel fiber. High fixation force prevents the drawing of fibers. The high anchoring force combined with the elongation at high peak loads prevents the drawing of the fiber, prevents the fiber from breaking and prevents brittle fracture of the concrete during tensioning. The higher the tensile strength and fixation force, the better the tensile strength can be utilized after cracking.

The steel section according to the invention, more particularly the central section of the middle of the steel fiber, has a tensile strength (R _m ) higher than 1000 MPa and elongation at maximum load (A _{g + e} ) of at least 2.5%, or a tensile strength of at least 1000 MPa, for example. (R _m ) and elongation at maximum load of at least 4% (A _{g + e} ). In a preferred embodiment, the steel section, more particularly the central section of the middle of the steel fiber, has a tensile strength (R _m ) of at least 1500 MPa and an elongation at maximum load (A _{g + e} ) of at least 2.5%, or a tension of at least 1500 MPa, for example. Strength (R _m ) and elongation (A _{g + e} ) at maximum load of at least 4%. In a more preferred embodiment, the steel section, more particularly the central section of the middle of the steel fiber, has a tensile strength (R _m ) of at least 2000 MPa and an elongation at maximum load (A _{g + e} ) of at least 2.5%, or at least 2000 MPa, for example. Tensile strength (R _m ) and elongation (A _{g + e} ) at maximum load of at least 4%. Fibers with high tensile strength (R _m ) can withstand high loads. Fibers characterized by elongation at high maximum load (A _{g + e} ) are CMOD exceeding 0.5 mm, exceeding 1.5 mm, exceeding 2.5 mm or exceeding 3 mm in a three-point bending test according to EN 14651. It is not broken at

The central section of the steel fibers, more particularly the middle of the steel fibers, typically has a diameter D between 0.10 mm and 1.20 mm, such as between 0.5 mm and 1 mm, more specifically 0.7 mm or 0.9 mm. If the cross section of the steel fiber, more particularly the central section of the middle part of the steel fiber is not round, the diameter is equal to the diameter of a circle having the same surface area as the cross section of the central section of the middle part of the steel fiber. Steel fibers typically have a ratio (ratio steel fiber length / D) of the length of the steel fiber divided by the diameter of the steel fiber, typically in the range from 40 to 100. The length of the steel fibers is for example 60 mm, 65 mm or 70 mm. The length of the steel fiber refers to the sum of the total length of the steel fiber, that is, the length of the center portion and the length of the fixing end or the fixing ends.

The steel fibers according to the present invention may be provided with any type of anchoring end, such as a thickened or expanded anchoring end, a nail head, a flattening anchoring end, a hook-shaped anchoring end, a bent or corrugated anchoring end or any combination thereof. .

Certain types of anchoring ends include anchoring ends biased from the main axis of the middle of the steel fiber. 'Deviation' means to deviate from a straight line, ie away from the major axis of the middle part of the steel fiber. A first example of steel fiber having a biased anchoring end includes an intermediate portion and an anchoring end provided at one or both ends of the intermediate portion. The middle part has a main axis. The anchoring end is deflected from the main axis in the first bent section. The first bent section has a first radius of curvature. Preferably the anchoring end comprises additional bending sections, such as a second bending section having a second radius of curvature and a third bending section having a third radius of curvature. Two consecutive bent sections may be directly connected to each other. As an alternative, the two bent sections can be connected by straight sections. By "continuous bending section" is meant a bending section that is continuous with each other. Preferably, when the steel fibers in a stable position on the horizontal plane are projected perpendicularly to the horizontal plane, the vertical projection plane in the horizontal plane of the at least two consecutive bent sections is located on one side of the vertical projection plane in the horizontal plane of the main axis of the intermediate part. "Stable position" means the position where the steel fibers adhere when the steel fibers are disposed on the horizontal plane.

Further examples of steel fibers provided with anchoring ends include steel fibers having an intermediate portion and anchoring ends provided at one or both ends of the intermediate portion. The middle part has a main axis. The anchoring end or anchoring ends comprise at least a first straight section, a second straight section and a third straight section. The first straight section, the second straight section and the third straight section each have a major axis. The first straight section is connected to the middle by the first bent section, the second straight section is connected to the first straight section by the second bent section, and the third straight section is connected by the third bent section to the second straight line. Is connected to the section. The first straight section, the second straight section and the third straight section each have a main axis, that is, a major axis of the first straight section, a major axis of the second straight section and a major axis of the third straight section. The included angle between the main axis of the middle portion and the main axis of the first straight section is between 100 and 160 degrees. The second straight section has a major axis substantially parallel to the major axis of the middle part.

The steel fiber according to the present invention may have one fixing end at one end of the intermediate portion. Preferably, the steel fibers have fixing ends according to the invention at both ends of the steel fibers. If the steel fibers have fixing ends at both ends of the intermediate portion, the two fixing ends may be the same or different.

In steel fibers having fixing ends at both ends of the intermediate portion, both fixing ends can be bent in the same direction from the main axis of the intermediate portion of the steel fiber (symmetric fibers). Alternatively, one fixing end may be bent in one direction from the major axis of the steel fiber while the other fixing end may be bent in an opposite direction from the major axis of the steel fiber (asymmetric fiber).

According to a second aspect, there is provided a reinforced concrete structure comprising a concrete structure reinforced with steel fibers according to the present invention. Reinforced concrete structures may or may not be reinforced with traditional reinforcements (such as pre-stressed or post-tensioned reinforcements) in addition to the steel fibers according to the present invention.

In the reinforced concrete structure reinforced with steel fiber according to the present invention, the residual bending tensile strength (f _{R, 3)} the residual bending tensile strength ratio divided by (f _{R, 1)} (the ratio _{f R, 3 / f R,} 1) Is preferably higher than 1, more preferably higher than 1.15 or higher than 1.2, for example 1.3. A small amount of steel fiber input, such as less than 1 vol%, less than 0.5 vol% or even 0.25 vol%, will reach this ratio even when steel fibers are used.

The residual bending tensile strength (f _{R , 3} ) of the reinforced concrete structure using the steel fiber according to the invention is preferably higher than 3.5 MPa, more preferably the residual bending tensile strength (f _{R , 3} ) is higher than 5 MPa. Or even higher than 6 MPa.

Fiber-reinforced concrete structures according to the invention can be used in ULSs exceeding 3 MPa, such as above 4 MPa, such as above 5 MPa, above 6 MPa, above 7 MPa, or above 7.5 MPa. It has a residual strength after an average crack of. By using the steel fibers according to the invention, concrete structures with residual strength after average cracking in ULS exceeding 3 MPa use C35 / 45 concrete and use less than 1 vol% or even less than 0.5 vol% Can be obtained. According to the present invention, the preferred reinforcement concrete structures have residual strength after average cracking in ULS above 5 MPa using C35 / 45 concrete and using less than 1 vol% or even less than 0.5 vol% input.

It should be noted that reinforcement concrete structures with residual strength after average cracking in ULS above 3 MPa or 5 MPa are present. However, these reinforcement concrete structures known in the art use large amounts of input steel (greater than 0.5 vol% or more than 1 vol%) in moderate strength concrete or high strength concrete, or use medium input high strength fibers in high strength concrete.

According to a third aspect, the use of the steel fibers according to the invention for load carrying structures of concrete is proposed.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.
1 shows a tensile test (load-strain test) of steel fibers.
2 shows a three point bending test (load-crack opening displacement curve or load-deflection curve).
3 shows a load-crack opening displacement curve.
4 and 5 illustrate embodiments of steel fibers that do not meet the requirements of the present invention.
6 and 7 show an embodiment of a steel fiber according to the present invention.

Although the present invention is described with reference to specific drawings and specific embodiments, the invention is not limited thereto but only by the claims. The drawings described are only schematic and are not restrictive. The dimensions of some of the elements in the figures may be exaggerated for illustrative purposes and may not be drawn to scale. Dimensions and relative dimensions do not correspond to the actual materialization of the present invention.

The following terms are only presented to aid the understanding of the present invention.

Maximum load capacity (F _m ): the maximum load the steel fiber will withstand during the tensile test,

Elongation at full load (%): expressed as a percentage of the original gauge length, the increase in gauge length of the steel fiber at maximum force,

% Elongation at break, expressed as a percentage of the original gauge length, the increase in gauge length at the moment of break,

Tensile strength (R _m ): stress corresponding to maximum load (F _m ),

-Stress: the original cross-sectional area of the force-breaking steel fiber,

-Input: amount of fiber added to concrete ((expressed as kg / ㎥ or vol% ((1 vol% corresponds to 78.50 kg / ㎥)),

-Normal strength concrete: concrete with a strength less than that of concrete of the C50 / 60 strength class specified in EN206,

High strength concrete: Concrete with a strength higher than that of concrete of the C50 / 60 strength class specified in EN206.

In order to demonstrate the invention, two different tests are carried out on a number of different steel fibers, namely the steel fibers of the prior art and the steel fibers according to the invention, as follows.

Tensile test (load-strain test)

3-point bending test (load-crack opening displacement curve or load-deflection curve)

Tensile tests are conducted on steel fibers, more specifically on the middle or central section of the steel fibers. As an alternative, the tensile test is conducted on the wire used to make the steel fibers. Tensile tests are used to determine the maximum load capacity (F _m ) of steel fibers and the elongation at maximum load (A _{g + e} ). The three-point bend test is carried out on notched reinforced beams specified in EN 14651. This test is used to determine the residual tensile strength. These tests are illustrated in FIGS. 1 and 2, respectively.

1 shows a test batch 60 of a tensile test (load-strain test) of steel fibers. With the help of test batch 60, steel fibers are tested for maximum load capacity (F _m ) (break load), tensile strength (R _m ) and total elongation at maximum load (A _{g + e} ). . First, the anchoring end (eg, an extended end or a hook-shaped end) of the steel fiber under test is cut. The middle portion 14 (or remaining center section) of the remaining steel fibers is fixed between the two pairs of clamps 62 and 63. The increased tensile force F is applied to the middle portion 14 of the steel fiber via the clamps 62, 63. The displacement or elongation due to this increased tensile force F is measured by measuring the displacement of the grips 64, 65 of the extensometer. L ₁ is the length of the middle portion 14 (or the remaining center section), for example 50 mm, 60 mm or 70 mm. L ₂ is the distance between the clamps, for example 20 mm or 25 mm. L ₃ is the gauge length of the extensometer and is at least 10 mm, such as 12 mm, such as 15 mm. In order to improve gripping to the middle portion 14 of the steel fibers of the extensometer, the middle portion (or central section) of the steel fibers may be coated or coated with a thin tape to prevent the extensometer from slipping on the steel fibers. The load-extension curve is recorded by this test. The total elongation at maximum load is calculated by the formula:

With the help of the arrangement 60 of FIG. 1, a number of different wires are subjected to a maximum load capacity (F _m ) (break load), tensile strength (R _m ) and total elongation at maximum load (A _{g + e} ). Conduct a test on Five tests are performed per sample. Table 1 gives an overview of the wire under test.

Wire type Carbon content Diameter (mm) F _m (N) R _m (MPa) A _{g + e} (%) One that 1.0 911 1160 1.86 2 that 0.9 751 1181 2.16 3 The 0.89 1442 2318 5.06 4 medium 0.75 533 1206 2.20 5 medium 0.90 944 1423 1.84

Low carbon steels are defined as steels having a carbon content of up to 0.15%, such as 0.12%, medium carbon steels are defined as steels having a carbon content between 0.15% and 0.44%, such as 0.18%, and high carbon steels are higher than 0.44%. It is defined as a steel having a carbon content, such as a carbon content of 0.5% or 0.6%.

2 shows an experimental setup 200 of a three point bending test. A three-point bending test was performed for 28 days in accordance with European standard EN 14651 using a spectroscopic sample 210 of 150 × 150 × 600 mm. In the midspan of the sample 210, a single notch 212 having a depth of 25 mm was engraved using a diamond blade to localize the cracks. The test batch includes two support rollers 214, 216 and one loading roller 218. This arrangement can operate in a controlled manner. That is, it may cause a certain ratio of displacement (CMOD or sag). This test was conducted at the displacement ratio specified in EN 14651. Load-crack opening displacement curves or load-deflection curves were recorded. An example of a load-crack opening displacement curve 302 is shown in FIG. 3.

Residual bending strengths f _{R , i} (i = 1, 2, 3, 4) are evaluated according to EN 14651. The residual bending tensile strength f _{R , 1} , f _{R , 3} is defined by the following crack opening displacement CMOD _i or midspan deflection δ _{R, i} , respectively.

CMOD ₁ = 0.5 mm δ _{R, 1} = 0.46 mm

CMOD ₃ = 2.5 mm δ _{R, 3} = 2.17 mm

Residual bending strength f _{R , i} (i = 1, 2, 3, 4) is evaluated according to EN 14651 and can be calculated by the following formula.

Where F _R , _i is the load corresponding to CMOD = CMOD _i or δ = δ _i (i = 1, 2, 3, 4),

b is the width of the sample in mm,

h _sp is the distance in mm between the tip of the notch and the top of the sample,

L is the span distance (mm) of a sample.

With the help of the arrangement 200 of FIG. 2, the performance of a number of different steel fibers is tested with regard to the determination of anchorage and fracture mechanisms. In this test, steel fibers are embedded in C35 / 45 concrete. Curing time was 14 days or 28 days. An overview of the steel fibers tested is given in Table 2. The test results are shown in Table 3. Steel fibers are characterized by the length of the steel fibers, the type of wire used to make the steel fibers, the diameter of the steel fibers (more specifically, the diameter of the middle or central section of the steel fibers) and the details of the anchoring ends. All steel fibers described in Table 2 have two fixing ends, namely, a first fixing end provided at one end and a second fixing end provided at the other end. If a flattening section is provided in the middle of the steel fiber, the middle has a flattening section for each anchoring end. That is, it has a first flattening section close to but not immediately adjacent to the first anchoring end and a second flattening section close to but not immediately adjacent to the second fixing end. FIB2 (FIG. 5) is a fiber having nail heads at both ends as a fixing end. FIB1, FIB3 and FIB4 have a fixing end having a first straight section, a second straight section and preferably a third straight section. There is a first bent section between the first straight section and the middle of the fixing end, there is a second bent section between the second straight section of the fixing end and the first straight section of the fixing end, and the third straight section of the fixing end And a third bending section between the second straight section of the anchoring end. Table 3 shows the number of straight sections at the anchoring end, the included angle between the major axis of the middle part and the major axis of the first straight section, the orientation of the second straight section towards the middle part, between the main axis of the second straight section and the major axis of the third straight section. Specify the details of the anchoring end, such as the angle of engagement, the orientation of the fourth straight section towards the middle. The geometries of the different fibers are shown in FIGS. 4, 5, 6 and 7. FIB1 (FIG. 4) and FIB2 (FIG. 5) are prior art fibers. FIB1 (FIG. 4) is a low carbon fiber having anchorage ends with two straight sections. FIB3 (FIG. 6) and FIB4 (FIG. 7) are fibers in accordance with the present invention.

Two straight sections with common vertices define two angles. The sum of these two angles is 360 degrees. For the purposes of the present invention, the minimum angle of two angles defined by two straight sections having a common vertex is referred to as the "pinched angle". This means that the included angle between the main axis of the intermediate part and the main axis of the first straight section is the minimum angle defined by the main axis of the intermediate part and the main axis of the first straight section. Similarly, the included angle between the main axis of the second straight section and the main axis of the third straight section is the minimum angle defined by the main axis of the second straight section and the main axis of the third straight section.

The prior art steel fiber (FIB1) is shown in FIG. The steel fiber 400 includes an intermediate portion 404 and a fixing end 402 provided at both ends of the intermediate portion 404. The intermediate portion 404 has a major axis 403. Each anchoring end includes a first bent section 405, a first straight section 406, a second bent section 407, and a second straight section 408. The included angle between the main axis 403 of the intermediate portion 404 and the main axis of the first straight section 406 is represented by α. The second straight section 408 is parallel or substantially parallel to the major axis of the intermediate portion 403.

The prior art steel fiber (FIB2) is shown in FIG. The steel fiber 500 includes an intermediate portion 504 and a fixing end 502 provided at both ends of the intermediate portion 504. The fixing end includes a nail head.

Steel fiber 600 (FIB3) shown in Figure 6 is a steel fiber according to the present invention. FIG. 6A is a plan view of a steel fiber, and FIG. 6B is a top view. The steel fiber 600 has an intermediate portion 604 provided with fixing ends 602 at both ends. The intermediate portion 604 has a major axis 603. In the middle portion 604 of the steel fiber 600 there are two flattening sections 601, namely a first flattening section close to but not immediately adjacent to the first anchoring end and a second flattening section close to but not immediately adjacent to the second anchoring end. Prepared. The first flattening section 601 has a predetermined length l _fl1 and the second flattening section 601 has a predetermined length l _fl2 . The distance between the first flattened section and the first anchoring end is for example 2 mm or 3 mm. Likewise the distance between the second flattened section and the second anchoring end is for example 2 mm or 3 mm. The middle portion 604 has a central section 610 located between the first flattened section and the second flattened section. The central section 610 has a length l '. The total length of the middle part is denoted by L, the length of the section located between the first anchoring end and the first flattening section, the length of the first flattening section l _fl1 , the length of the central section l ', the second flattening section Corresponds to the sum of the length l _fl2 and the length of the section located between the second flattened section and the second anchoring end.

Each anchoring end 602 includes a first bent section 605, a first straight section 606, a second bent section 607, and a second straight section 608. Both fixing ends are bent in the same direction from the main axis 603 of the intermediate portion 604. The included angle between the main axis 603 of the intermediate portion 604 and the main axis of the first straight section 606 is represented by α. The second straight section 608 is parallel or substantially parallel to the major axis 603 of the intermediate portion 604.

Figure 7 shows a further embodiment (FIB4) of a steel fiber 700 according to the present invention. 7A is a top view of the steel fiber and FIG. 7B is a top view. The steel fiber 700 has an intermediate portion 704 provided with fixing ends 702 at both ends. The intermediate portion 704 has a major axis 703. In the middle portion 704 of the steel fiber 700 there are two flattening sections 701, a first flattening section close to the first anchoring end but not immediately adjacent and a second flattening section near the second anchoring end but not immediately adjacent. Prepared. The first flattening section 701 has a predetermined length l _fl1 and the second flattening section 701 has a predetermined length l _fl2 . The distance between the first flattened section and the first anchoring end is for example 2 mm or 3 mm. Likewise, the distance between the second flattened section and the second anchoring end is for example 2 mm or 3 mm. The middle portion 704 has a central section 710 located between the first flattened section and the second flattened section. The central section 710 has a length l '. The total length of the middle part is denoted by L, the length of the section located between the first anchoring end and the first flattening section, the length of the first flattening section l _fl1 , the length of the central section l ', the second flattening section Corresponds to the sum of the length l _fl2 and the length of the section located between the second flattened section and the second anchoring end.

Each anchoring end 702 has a first bent section 705, a first straight section 706, a second bent section 707, a second straight section 708, a third bent section 709 and a third Straight section 712. Both fixing ends are bent in the opposite direction from the main axis 703 of the intermediate portion 704. The included angle between the major axis 703 of the intermediate portion 704 and the major axis of the first straight section 706 is represented by α. The included angle between the major axis of the second straight section 706 and the major axis of the third straight section 708 is represented by β. The second straight section 708 is parallel or substantially parallel to the major axis 703 of the intermediate portion 704.

fiber
type Length
(mm) wire
type diameter
(mm) Flattening section
(The presence or absence) Straight
Number of sections alpha
(Angle) Second section parallel to the major axis of the middle
(The presence or absence) beta
(Angle) drawing FIB1 60 2 0.90 radish 2 140 U Of 4 FIB2 54 One 1.00 radish Of Of Of Of 5 FIB3 60 3 0.89 U 2 140 U Of 6 FIB4 60 3 0.89 U 3 140 U 140 7

α: included angle between the main axis of the middle portion and the main axis of the first straight section

β: included angle between the main axis of the second straight section and the main axis of the third straight section

Fiber type input
(kg / m3) Curing time
(Days) f _L f _{R , 1} f _{R , 2} f _{R , 3} f _{R , 3} / f _{R , 1} FIB1 40 28 5.48 3.75 3.85 3.68 0.98 FIB2 40 28 5.80 4.11 4.31 2.83 0.69 FIB3 40 28 5.80 4.88 6.21 6.47 1.33 FIB3 20 28 5.68 3.06 3.83 4.23 1.38 FIB4 40 14 5.11 4.80 6.14 6.48 1.35

From Table 3 it can be concluded that the ratio of the prior art fibers (FIB1 and FIB2) (f _{R , 3} / f _{R , 1} ) is less than one. In addition, the residual bending tensile strengths f _{R , 1} , f _{R , 2} , f _{R , 3} of the fibers of the prior art (FIB1 and FIB2) are low. That is, it is significantly lower than the residual bending tensile strength (f _{R , 1} , f _{R , 2} , f _{R , 3} ) of FIB3. Since the hardening time of steel fibers FIB1, FIB2 and FIB3 is 28 days while the hardening time of steel fiber FIB4 is only 14 days, the residual bending tensile strengths of FIB1, FIB2 and FIB3 (f _{R , 1} , f _{R, 2} , f _{R , 3} ) Cannot be directly compared with the residual bending tensile strength (f _{R , 1} , f _{R , 2} , f _{R , 3} ) of FIB4. In the case of steel fibers (FIB3, FIB4) according to the invention, the ratio (f _{R , 3} / f _{R , 1} ) is greater than one.

For steel fiber (FIB3), the test is carried out with two different inputs, 20 kg / m 3 and 40 kg / m 3. Even when a fiber input of 20 kg / m ₃ is used, the ratio f _{R, 3} / f _{R, 1} exceeds 1. This means that these steel fibers exhibit the same behavior as traditional reinforcing bars (strain-strain strains, not stress-crack opening strains).

When a pull test is performed on the steel fibers of Table 2 to determine the fixing force, the fixing force in the concrete of the steel fibers FIB3 and FIB4 is higher than that of the steel fibers FIB1 and FIB2.

Compared to the steel fibers having the same geometry and steel composition as the steel fibers (FIB3, FIB4) but having no flattening section, the steel fibers (FIB3, FIB4) having the flattening sections are the flattening sections. It has a higher anchorage in concrete than steel fibers without.

By way of example, the steel fibers according to the invention can be produced as follows. The starting material is for example a wire rod having a diameter of 5.5 mm or 6.5 mm, and for example a minimum carbon content of at least 0.50 wt% (wt%), such as at least 0.60 wt%, a manganese content of 0.20 wt% to 0.80 wt%, from 0.10 wt% to Steel composition having a silicon content of 0.40 wt%. The sulfur content is up to 0.04 wt% and the phosphorus content up to 0.04 wt%. Typical steel compositions comprise 0.725% carbon, 0.550% manganese, 0.250% silicon, 0.015% sulfur and 0.015% phosphorus. Alternative steel compositions include 0.825% carbon, 0.520% manganese, 0.230% silicon, 0.008% sulfur and 0.010% phosphorus. The wire rod is cold drawn in a number of drawing stages until the final diameter is between 0.20 mm and 1.20 mm. Where high elongation at break and / or elongation at maximum load is required, stress-relaxing treatment of fresh wire may be performed, for example, by passing the wire through a high frequency or medium frequency induction coil having a length adapted to the wire's passage speed. It may be desirable. Applying heat treatment at a temperature of about 300 [deg.] C. for a predetermined time was observed to reduce the tensile strength by about 10% without increasing the elongation at break and elongation at maximum load. However, increasing the temperature slightly above the temperature of 400 ° C., further decrease in tensile strength is observed, while increasing the elongation at break and the elongation at maximum load.

The wire may or may not be coated with a corrosion resistant coating such as a zinc or zinc alloy coating, more particularly a zinc aluminum coating or a zinc aluminum magnesium coating. To facilitate drawing, the wire may be coated with a copper or copper alloy coating prior to or during drawing.

The strain relaxed wire is then cut into steel fibers of appropriate length, and the ends of the steel fibers are provided with suitable anchors or thickness extensions. Cutting and hook forming can be performed in one and the same work step using a suitable roll.

The steel fibers thus obtained may or may not be bonded to one another in accordance with US-A-4284667.

In addition or in lieu thereof, the obtained steel fibers may be arranged in a chain package according to EP-B1-1383634 or in a belt-like package as disclosed in the applicant's European patent application 09150267.4.

Claims (15)

Steel fiber for concrete or mortar reinforcement,
An intermediate portion having a predetermined length L, a first fixing end provided at one end of the intermediate portion, and a second fixing end provided at the other end of the intermediate portion, the intermediate portion having a first flattening section and a second flattening A section and a central section, wherein the central section is located between the first flattened section and the second flattened section and the first flattened section is located close to but not immediately adjacent to the first anchoring end. Located close to but not immediately adjacent to the second anchoring end, the central section has a length (l '), the central section having a tensile strength (R _m ) of at least 1000 MPa and an elongation at maximum load of at least 2.5% With (A _{g + e} )
Steel fiber for concrete or mortar reinforcement. The ratio (ratio l '/ L) of the length (l') of the center section divided by the length (L) of the middle section is higher than 0.50.
Steel fiber for concrete or mortar reinforcement. The method of claim 1, wherein the intermediate portion of the steel fiber has a tensile strength (R _m ) of at least 1500 MPa.
Steel fiber for concrete or mortar reinforcement. 3. The method according to claim 1, wherein the intermediate portion of the steel fiber has an elongation (A _{g + e} ) at maximum load of at least 4%.
Steel fiber for concrete or mortar reinforcement. The distance between the first anchoring end and the first flattening section and / or the distance between the second anchoring end and the second flattening section is between 0.5 mm and 20 mm. Saiin
Steel fiber for concrete or mortar reinforcement. The method according to any one of claims 1 to 5, wherein the first flattened section has a length (l _f1) and the second flattened section has a length (l _f2), and the length (l _f1) The length l _f2 is between 0.5 mm and 10 mm
Steel fiber for concrete or mortar reinforcement. The flattening section according to any one of claims 1 to 6, wherein the flattening section is flattened in a plane substantially parallel to the plane of the steel fibers.
Steel fiber for concrete or mortar reinforcement. The flattening section according to claim 1, wherein the flattening section is flattened in a plane substantially perpendicular to the plane of the steel fibers.
Steel fiber for concrete or mortar reinforcement. The steel fiber according to any one of claims 1 to 8, wherein the steel fiber has a diameter (D) between 0.1 mm and 1.20 mm.
Steel fiber for concrete or mortar reinforcement. The ratio (= ratio steel fiber length / D) of the length of the steel fiber divided by the diameter of the steel fiber is between 40 and 100.
Steel fiber for concrete or mortar reinforcement. The steel fiber according to any one of claims 1 to 10, wherein the steel fiber is in a stress relaxation state. Reinforced with steel fibers according to one or more of the preceding claims.
Concrete structures. The method according to claim 12, wherein the ratio of dividing residual bending tensile strength (f _{R , 3} ) by residual bending tensile strength (f _{R , 1} ) (= ratio f _{R , 3} / f _{R , 1} ) is 1. Concrete structures higher than 1 when less than vol%. The concrete structure according to claim 12 or 13, wherein the residual bending tensile strength (f _{R , 3} ) is higher than 5 MPa when the input amount of the steel fiber is less than 1 vol%. Use of steel fibers for reinforcing concrete or mortar according to claim 1 for load-bearing structures of concrete.

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