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    • 专利摘要:
    The invention relates to a steel fiber for reinforcing concrete or mortar. The steel fiber has a center portion and an anchor end at one or both ends of the center portion. The anchor end includes at least a first straight section, a first curved section, a second straight section, a second curved section, and a third straight section. The invention furthermore relates to a concrete structure containing steel fibers according to the present invention, and to the use of steel fibers for structural applications.
    公开号:BE1021498B1
    申请号:E2011/0718
    申请日:2011-12-13
    公开日:2015-12-03
    发明作者:Ann Lambrechts；Haeke Martin Van
    申请人:Nv Bekaert Sa；
    IPC主号:
    专利说明:

    Steel fiber for reinforcing concrete or mortar, with an anchor end with at least three straight sections
    Description
    Technical field The invention relates to steel fibers for reinforcing concrete or mortar. The steel fibers are provided with anchoring ends that make it possible to obtain good anchoring when they are embedded in concrete or in mortar. The steel fibers according to the present invention are provided with at least one anchoring end with at least three straight sections. The steel fibers according to the present invention have a good effect in the service limit state (service ability limit state or SLS) and in the extreme limit state (ultimate limit state or ULS) when they are embedded in concrete or mortar. The invention furthermore relates to concrete or mortar structures containing such steel fibers.
    State of the art Concrete is a brittle material with a low tensile strength and a limited elongation. In order to improve the properties of concrete, such as tensile strength and tensile strength, concrete reinforced with fibers and more specifically concrete reinforced with metal fibers was designed.
    It is known in the prior art that the properties of the fibers, such as the fiber concentration, the fiber geometry, and the fiber aspect ratio, exert a great influence on the final behavior of the reinforced concrete.
    With regard to fiber geometry, it is known that fibers that have a shape that is different from a straight shape, realize a better anchoring of the fibers in the concrete or in the mortar. In addition, it is known that fibers that do not tend to form balls when they are added to or mixed with concrete or mortar are preferred.
    Various examples of different fiber geometries are known in the art. There are examples of fibers that are provided with undulations, over the full length or over a part of their length. Examples of steel fibers which are provided with undulations over their entire length are described in document WO84 / 02732. There are also known fibers in the prior art which are provided with hook-shaped ends. Such fibers are described, for example, in the document US 3,942,955.
    Similarly there are fibers whose cross-sectional profile is not constant along the length, such as fibers that are provided with thicker and / or flattened sections.
    An example of a steel fiber provided with thicker sections is a steel fiber with thickenings in the form of a nail head at each of the ends, as described in the document US 4,883,713.
    Japanese patent 6-294017 describes the flattening of a steel fiber over its full length. The German utility model G9207598 describes the flattening of only the middle part of a steel fiber with hook-shaped ends. The document US 4,233,364 describes straight steel fibers which are provided with ends which are flattened and provided with a flange in a plane which is substantially perpendicular to the flattened ends.
    Steel fibers with flattened angular ends are known from the documents EP 851957 and EP 1282751.
    Known fibers from the prior art for reinforcing concrete function very well in the known fields of application such as industrial floors, sprayed concrete, road structures, ...
    However, the disadvantage of fibers known today from the prior art is the relatively limited performance in the extreme limit state (ULS) when use is made of moderate fiber dosages. For more demanding structural applications, such as beams and plates, high dosages, typically 0.5 vol.% (40 kg / m3) and higher and exceptionally up to 1.5 vol.% (120 kg / m3) are used to provide the necessary performance in the extreme limit state ( ULS). These high dosages make it difficult to mix and apply concrete reinforced with steel fibers. Some of the prior art fibers do not work at all in ULS because they break at crack width opening displacements (CMODs) or crack widths that are lower than those required in ULS. Other fibers, such as fibers with hook-shaped ends, do not perform well in ULS because they are designed to be pulled out.
    Description of the Invention It is an object of the present invention to provide steel fibers for reinforcing concrete or mortar, with which the drawbacks of the prior art can be avoided.
    It is another object to provide steel fibers capable of bridging crack widths larger than 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, or even larger than 3 mm during a three-point bend test according to the European Standard EN 14651 (June 2005).
    It is yet another object of the present invention to provide steel fibers that exhibit good anchoring in concrete or mortar.
    It is an additional object to provide steel fibers that do not tend to form balls when they are added to the concrete or mortar.
    In addition, it is an object of the present invention to provide steel fibers that can be used in interesting ways for structural applications in which the steel fibers are used in low to medium dosages, typically 1% steel fibers or 0.5% steel fibers.
    Moreover, it is yet another object to provide steel fibers that make it possible to avoid or reduce the creep behavior of cracked concrete.
    According to a first aspect of the present invention, there is provided a steel fiber for reinforcing concrete or mortar.
    The steel fiber comprises a middle part and an anchoring end at one or both ends of the middle part. The middle part has a main axis. The anchor end or anchor ends is or are provided with at least a first, a second, and a third straight section. Each of the straight sections has a major axis, respectively, the major axis of the first straight section, the major axis of the second straight section, and the major axis of the third straight section.
    The first straight section is connected to the center portion of the stake fiber by means of a first curved section; the second straight section is connected to the first straight section by means of a second curved section; the third straight section is connected to the second straight section through a third curved section.
    This means that the first straight section is bent away from the middle part by the first bent section; the second straight section is bent away from the first straight section through the second bent section, and the third straight section is bent away from the second straight section through the third bent section.
    The first straight section bends away from the main axis of the middle section, thereby defining an enclosed angle between the main axis of the middle section and the main axis of the first straight section.
    The second straight section is substantially parallel to the main axis of the middle part.
    The third straight section bends away from the main axis of the middle part, in the same direction as the first straight section bends away from the main axis of the middle part, thereby defining an enclosed angle between the main axis of the second straight section and the main axis of the third straight section.
    The enclosed angle between the main axis of the middle part and the main axis of the first straight section is preferably between 100 and 160 degrees. The enclosed angle between the major axis of the second straight section and the major axis of the third straight section is preferably between 100 and 160 degrees.
    As already mentioned above, the second straight section is substantially parallel to the main axis of the middle part. By the term "substantially parallel" it is meant here that there may be some deviation from a parallel position. However, if there is a deviation, this deviation is either minor or accidental. By "a small deviation" is meant here that the deviation relative to a parallel position is less than 15 degrees, and preferably less than 10 degrees.
    Two enclosed straight sections with a common angle define two angles. The sum of these two angles is 360 degrees. For this invention, the smaller of these two angles is defined by two straight sections with a common angle defined as the "enclosed angle".
    This means that the enclosed angle between the main axis of the middle part and the main axis of the first straight section is defined as the smallest angle formed by the main axis of the middle part and the main axis of the first straight section. Similarly, the included angle between the major axis of the second straight section and the major axis of the third straight section is defined as the smallest angle formed by the major axis of the second straight section and the major axis of the third straight section.
    As already mentioned above, the enclosed angle between the main axis of the middle part and the main axis of the first straight section is preferably between 100 and 160 degrees. This means that the angle that is complementary to the included angle between the main axis of the middle part and the main axis of the first straight section is between 20 and 80 degrees.
    If the enclosed angle between the main axis of the middle part and the main axis of the first straight section is greater than 160 degrees (or if the complementary angle of this enclosed angle is less than 20 degrees), the anchoring in concrete or mortar is limited and is also the performance in SLS and in ULS is poor. Such a fiber tends to be pulled out.
    If the enclosed angle between the main axis of the middle part and the main axis of the first straight section is less than 100 degrees (or if the complementary angle of this enclosed angle is greater than 80 degrees), the fibers coagulate and do not mix homogeneously in the concrete or in the mortar.
    Preferably, the enclosed angle between the main axis of the middle part and the main axis of the first straight section is between 110 and 160 degrees (and accordingly the complementary angle is between 20 and 70 degrees), e.g. between 120 and 160 degrees (and accordingly the complementary angle is between 20 and 60 degrees), for example 150 degrees (correspondingly the complementary angle is 30 degrees), or 140 degrees (correspondingly the complementary angle is 40 degrees).
    Similarly, the included angle between the major axis of the second straight section and the major axis of the third straight section is preferably between 100 and 160 degrees. This means that the angle that is complementary to the included angle between the second straight section and the main axis of the third straight section is between 20 and 80 degrees. If the enclosed angle between the main axis of the second straight section and the main axis of the third straight section is greater than 160 degrees (or if the complementary angle of this enclosed angle is less than 20 degrees), the anchoring in concrete or mortar is limited and also the performance in SLS and ULS is poor. Such a fiber tends to be pulled out.
    If the enclosed angle between the main axis of the second straight section and the main axis of the third straight section is less than 100 degrees (or if the complementary angle to this enclosed angle is greater than 80 degrees), the fibers coagulate and do not mix homogeneously in the concrete or in the mortar.
    It is better if the enclosed angle between the main axis of the second straight section and the main axis of the third straight section is between 110 and 160 degrees (and accordingly the complementary angle is between 20 and 70 degrees), e.g. between 120 and 160 degrees (accordingly the complementary angle is between 20 and 60 degrees), for example 150 degrees (accordingly the complementary angle is 30 degrees) or 140 degrees (accordingly the complementary is 40 degrees).
    The enclosed angle between the main axis of the middle part and the main axis of the first straight section, and the enclosed angle between the main axis of the second straight section and the main axis of the third straight section may be the same or different.
    In one embodiment, the enclosed angle between the main axis of the middle section and the main axis of the first straight section, and the enclosed angle between the main axis of the second straight section and the main axis of the third straight section are the same or substantially the same. In this particular embodiment, the major axis of the first straight section and the major axis of the third straight section are mutually parallel or substantially parallel.
    In certain embodiments of the present invention, the anchoring end is furthermore provided with a fourth straight section. This fourth straight section is connected to the third straight section by a fourth curved section. This means that the fourth straight section bends away from the third straight section through the fourth curved section. It is preferable, but not necessary, for the fourth straight section to be parallel to the major axis of the middle section and the major axis of the second straight section.
    A steel fiber that has four straight sections, with the second and fourth straight sections parallel to the main axis of the middle section, provides a very good performance in SLS and in ULS when embedded in concrete or mortar.
    In an alternative embodiment, the second straight section has a major axis that is substantially parallel to the major axis of the center portion of the steel fiber, and the fourth straight section is not parallel to the major axis of the center portion of the steel fiber. In the corresponding case, the angle between the fourth straight section and the main axis of the middle part is between -60 and +60 degrees, for example between -45 and +45 degrees, or between -30 and +30 degrees.
    The anchoring end of a steel fiber according to the present invention is provided with at least three straight sections.
    In principle there is no limit on the number of straight sections of an anchor end. However, the most preferred embodiments are provided with an anchoring end with three straight sections, four straight sections, five straight sections, or six straight sections. In each of these embodiments, there is a curved section between every two consecutive straight sections. Surprisingly, it was found that an anchor end having three straight sections and four straight sections provided the best performance when embedded in concrete or mortar, both in a pull-out test and in a three-point bending test.
    The straight sections, for example the first, second, third, and / or fourth straight sections, preferably have a length between 0.1 mm and 8 mm, and preferably between 0.1 mm and 5 mm, for example 0.5 mm or 2 mm.
    The lengths of the different straight sections can be selected independently of each other. This means that the different straight sections can have the same or different lengths.
    In preferred embodiments, the length of the different straight sections is the same.
    An example comprises a steel fiber with a first, second, third, and fourth straight section, all straight sections having a length of 2 mm.
    An alternative example comprises a steel fiber with a first straight section with a length of 0.5 mm, a second straight section with a length of 2 mm, a third straight section with a length of 0.5 mm, and a fourth straight section with a length of 2 mm.
    Each curved section has a radius of curvature: the first curved section has a first curvature radius, the second curved section has a second curvature radius, the third curved section has a third curvature radius, and the fourth curved section (if any) has a fourth curvature radius .
    The radius of curvature of the curved sections is preferably between 0.1 mm and 5 mm, for example between 0.5 mm and 3 mm, for example 1 mm, 1.2 mm, or 2 mm.
    The curvature radii of the different curved sections of the steel fiber can be selected independently of each other. This means that the radius of the first curved section, of the second curved section, of the third curved section, and of the fourth curved section (if any) can be the same or different.
    A steel fiber according to the present invention can be provided with an anchoring end at one end of the middle part. A steel fiber is preferably provided with an anchoring end at both ends of the middle part. In the case that the steel fiber is provided with an anchoring end at both ends of the middle part, the two anchoring ends may be the same or different.
    For a steel fiber with an anchoring end at both ends of the middle part, both anchoring ends can bend away in the same direction with respect to the main axis of the middle part of the steel fiber (symmetrical fibers).
    On the other hand, one anchoring end can bend away in a particular direction with respect to the main axis of the middle part of the steel fiber, while the other anchoring end bends away in the opposite direction with respect to the main axis of the middle part of the steel fiber (asymmetrical fibers).
    For a steel fiber according to the present invention, the middle part and the anchoring end are preferably situated in one plane, or they are situated substantially in one plane.
    The other anchor end, if present, may be located in the same plane or in a different plane.
    An advantage of steel fibers according to the present invention is that they do not coagulate when mixed with concrete or mortar. This results in a homogeneous distribution of the steel fibers in the concrete or mortar.
    The steel fibers according to the present invention function particularly well both in the use limit state (SLS) of a concrete or mortar structure, and in the extreme limit state (ULS) when used in a moderate or low dose, i.e. a dose of less than 1 vol% or less than 0.5 vol%, for example 0.25 vol%.
    It is known in the prior art that driving up the amount of fibers in concrete has a positive influence on the operation of the concrete reinforced with fibers.
    A major advantage of the present invention is that a good performance is achieved in SLS and ULS, with moderate or low doses of steel fibers. The material property used in the context of this invention for evaluating the performance in ULS and SLS of concrete reinforced with fibers is the residual flexural tensile strength. The residual flexural tensile strength is derived from the load at a predetermined tear width (CMOD) or deflection (5R).
    The residual bending tensile strengths are determined by using a three-point bending test in accordance with the European Standard EN 14651 (described further below in this application).
    The residual flexural tensile strength fR1 is determined at CMODi = 0.5 mm (5r, i = 0.46 mm), the residual flexural tensile strength fRi2 is determined at CMOD2 = 1.5 mm (5r, 2 = 1.32 mm), the residual flexural tensile strength fR, 3 is determined at CMOD3 = 2.5 mm (5r, 3 = 2.17 mm), the residual flexural tensile strength fRi4 is determined at CMOD4 = 3.5 mm (Ör, i = 3.02 mm).
    The residual bending tensile strength fR, i is the most important requirement for SLS design.
    The residual flexural tensile strength fR.3 is the most important requirement for ULS design.
    For steel fibers according to the present invention - in contrast to the steel fibers known from the prior art - the ratio between the residual flexural tensile strength fR, 3 and the residual flexural tensile strength fR, i (fR, 3 / fR, i) high even when low or moderate doses of steel fibers are used, such as, for example, doses that are less than 1 vol% or doses that are less than 0.5 vol%, for example 0.25 vol%.
    For fibers according to the present invention, the ratio fR, 3 / fR, i is preferably greater than 1, and even better greater than 1.05 or greater than 1.15, for example 1.2 or 1.3, when dosages are used that are less than 1 vol% or dosages which are less than 0.5 vol%, for example 0.25 vol%.
    For concrete reinforced with steel fibers according to the present invention with a dosage of 0.5 vol%, and where use is made of a C35 / 45 concrete, the residual flexural tensile strength fR, 3 is preferably greater than 3.5 MPa, greater than 5 MPa or even larger than 6 MPa, for example 7 MPa.
    Fibers known in the art, such as, for example, steel fibers with conically shaped ends (nail heads) produced from low carbon steel, work very well to limit the cracks to about 0.5 mm (SLS). However, these fibers exhibit low performance in ULS. This type of steel fiber breaks at crack widths (CMODs) that are smaller than those required for ULS.
    The ratio fR, 3 / fR, i is less than 1 for moderate dosages in a concrete of normal strength, for example a C35 / 45 concrete.
    Other fibers which are known from the prior art are fibers with hook-shaped ends, as for instance known from the document EP 851957, are designed to be pulled out.
    Also for this type of fiber, the ratio fR, 3 / îr, i is less than 1 for moderate dosages in a concrete of normal strength. MAXIMUM LOAD CAPACITY Fm - STRENGTH STRENGTH Rm A steel fiber according to the present invention, in particular the middle part of a steel fiber according to the present invention, preferably has a high maximum load capacity Fm. The maximum load capacity Fm is the largest load that the steel fiber can withstand during a tensile test. The maximum load capacity Fm of the middle part is directly related to the tensile strength Rm of the middle part because the tensile strength Rm is the maximum load capacity Fm divided by the area of the original cross section of the steel fiber.
    For a steel fiber according to the present invention, the tensile strength of the middle part of the steel fiber is preferably above 1000 MPa and more particularly above 1400 MPa, for example above 1500 MPa, for example above 1750 MPa, for example above 2000 MPa, for example above the 2500 MPa.
    The high tensile strength of the steel fibers according to the present invention makes it possible for the steel fibers to withstand high loads.
    A high tensile strength therefore results in a lower dosage of the fibers. However, using steel fibers that have a high tensile strength is only meaningful if the steel fibers have a good anchoring in the concrete.
    STRETCH AT MAXIMUM TAX
    According to a preferred embodiment, a steel fiber according to the present invention, in particular the middle part of a steel fiber, has an elongation at maximum load, Ag + e, of at least 2.5%. According to certain embodiments of the present invention, the center portion of the steel fiber has a maximum load elongation, Ag + e, that is greater than 2.75%, greater than 3.0%, greater than 3.25%, greater than 3.5%, greater than 3.75%, greater than 4.0%, greater than 4.25%, greater than 4.5%, greater than 4.75%, greater than 5.0%, greater than 5.25%, greater than 5.5%, greater than 5.75%, or even greater than 6.0%.
    In the context of the present invention, the elongation at maximum load, Ag + e, and not the elongation at break At is used to characterize the elongation of a steel fiber.
    The reason for this is that once the maximum load has been reached, there is a constriction of the available surface area of the steel fiber, and higher loads are no longer included.
    The elongation at maximum load, Ag + e, is the sum of the plastic elongation at maximum Ag, and of the elastic elongation.
    The elongation at maximum load does not include the structural elongation As that can be caused by the wavy character of the middle part of the steel fiber (if present). In the case of a wavy steel fiber, the steel fiber is first straightened before the Ag + e is measured.
    The high degree of elongation at the maximum load Ag + e can be obtained by applying a specific stress-removing or tempering treatment, such as a thermal treatment, to the steel wires from which the steel fibers will be produced. In this case, at least the middle part of the steel fiber is in an annealed state.
    Steel fibers with high toughness or high elongation at maximum load are preferred because these fibers will not break at CMODs that are greater than 0.5 mm, greater than 1.5 mm, greater than 2.5 mm, or greater than 3.5 mm in the three-point bending test according to EN 14651.
    ANCHORING POWER
    Preferably the steel fiber according to the present invention has a high degree of anchoring in the concrete or in the mortar.
    By providing the central part of the steel fiber with anchoring ends according to the present invention, the anchoring of the steel fibers in the concrete or in the mortar is significantly improved.
    A high degree of anchoring will prevent the fibers from being pulled out.
    A high degree of anchoring, combined with a high elongation at maximum load, will prevent the fibers from being pulled out, prevent fiber breakage, and prevent brittle fractures of concrete.
    A high degree of anchoring, combined with a high tensile strength, makes it possible to make better use of the tensile strength after the occurrence of cracks.
    For example, steel fibers according to the present invention have a tensile strength Rm that is higher than 1000 MPa, and an elongation at the maximum load Ag + e of at least 1.5%, a tensile strength Rm of at least 1000 MPa and an elongation at the maximum load Ag + e of at least 2.5%, a tensile strength Rm of at least 1000 MPa and of an elongation at the maximum load Ag + e of at least 4%.
    In a preferred embodiment, the steel fibers have a tensile strength Rm of at least 1500 MPa and of an elongation at the maximum load Ag + e of at least 1.5%, of a tensile strength Rm of at least 1500 MPa and of an elongation at the maximum Ag + e load of at least 2.5%, a tensile strength Rm of at least 1500 MPa and an elongation at the maximum load Ag + e of at least 4%.
    In additional preferred embodiments, the steel fibers have a tensile strength Rm of at least 2000 MPa and an elongation at the maximum load Ag + e of at least 1.5%, a tensile strength Rm of at least 2000 MPa and an elongation at the maximum load Ag + e of at least at least 2.5%, a tensile strength Rm of at least 2000 MPa and an elongation at the maximum load Ag + e of at least 4%.
    Fibers with a high tensile strength Rm can withstand high loads. Fibers characterized by a high elongation at the maximum load Ag + e will not break at CMODs that are higher than 0.5 mm, higher than 1.5 mm, higher than 2.5 mm, or higher than 3 mm in the three-point bending test according to EN 14651.
    The central portion of the steel fiber can be straight or linear, or it can be wavy or bent. In the case that the center portion is corrugated or undulated, the major axis of the center portion is defined as the line that intersects the wavy or undulating center portion in such a way that the total area of the upper wave portions or shallows above this line is the same as the total area of the waves or undulations below this line.
    The steel fibers, in particular the middle part, can have any cross-section, such as a circular cross-section, a substantially circular cross-section, a rectangular cross-section, a substantially rectangular cross-section, an oval cross-section, a substantially oval cross-section, ...
    The steel fibers, and more particularly the center parts of the steel fibers, typically have a diameter that is between 0.10 mm and 1.20 mm, for example between 0.5 mm and 1 mm or between 0.7 mm and 0.9 mm. In the case that the cross-section of the steel fiber, and more particularly of the center part of the steel fiber is not round, the diameter is equal to the diameter of a circle with the same area as the cross-section of the center part of the steel fiber.
    The steel fiber steel fiber typically exhibits a ratio of the length to the diameter L / D which is between 40 and 100. The length of the steel fibers is, for example, 50 mm, 55 mm, 60 mm, or 65 mm.
    By "length of a steel fiber" is meant the total length of the steel fiber, i.e. the sum of the length of the middle part and of the length of the anchoring end or of the anchoring ends.
    The middle part preferably has a length greater than 25 mm, for example greater than 30 mm, greater than 40 mm, or greater than 45 mm.
    The steel fiber or a part of the steel fiber can be flattened or can be provided with one or more flattened sections. For example, the middle part, a part of the middle part, an anchoring end, or a part of anchoring end can be flattened or provided with one or more flattened sections. Combinations can also be taken into consideration.
    If the middle part is provided with one or more flattened sections, the flattened section or sections is preferably located close to the anchoring end or the anchoring ends, but not immediately adjacent thereto.
    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. The reinforced concrete structure may or may not be reinforced with traditional reinforcement (for example, prestressed or post-tensioned reinforcement) on top of the steel fibers according to the present invention.
    For a reinforced concrete structure reinforced with steel fibers according to the present invention, the ratio between the residual flexural tensile strength sterkter, 3 and the residual flexural tensile strength rr, i (îr, 3 / îr, i) is preferably greater than 1, and better greater than 1.05, greater than 1.15, or greater than 1.2, for example 1.3. This ratio is achieved with low doses of steel fibers, for example a dose of steel fibers that is less than 1 vol%, or a dosage that is less than 0.5 vol%, or even with a dosage of 0.25 vol%.
    The residual flexural tensile strength fRi3 of a reinforced concrete structure using the steel fibers of the present invention is preferably greater than 3.5 MPa, greater than 4.5 MPa, greater than 5 MPa, or even greater than 6 MPa.
    The concrete structure reinforced with fibers according to the present invention has an average residual tear strength in ULS that is greater than 3 MPa, for example greater than 4 MPa, for example greater than 5 MPa, 6 MPa, 7 MPa, 7.5 MPa. By using steel fibers according to the present invention, concrete structures can be realized with an average residual tear strength in ULS that is greater than 3 MPa or greater than 4 MPa, and this by using C35 / 45 concrete and by using making fiber dosages that are less than 1 vol% or even less than 0.5 vol%.
    According to the present invention, preferred reinforced concrete structures have an average residual tear strength in ULS that is greater than 5 MPa, using C35 / 45 concrete and fiber dosages that are less than 1 vol% or even less than 0.5 vol%.
    It is important to note that reinforced concrete structures with an average residual tear strength exist in ULS greater than 3 MPa or greater than 5 MPa. These reinforced concrete structures, which are known in the art, however, use high doses of steel fibers (greater than 0.5 vol% or greater than 1 vol%) when using normal-strength concrete or high-strength concrete , or when moderate dosages of strong fibers in high-strength concrete are used.
    According to a third aspect, provision is made for the use of steel fibers according to the present invention for carrying out structural applications, i.e. load-bearing concrete structures.
    BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail below with reference to the accompanying drawings in which:
    Figure 1 gives an illustration of a tensile test (strain load test) on a steel fiber;
    Figure 2 gives an illustration of a three-point bend test (load-tear-width curve or load-deflection curve);
    Figure 3 gives an illustration of a load-crack width curve;
    Figures 4a, 4b, 4c, 4d, and 4th are illustrations of a number of different embodiments of prior art steel fibers and steel fibers provided with anchoring ends according to the present invention.
    Embodiments of the Invention The present invention will be described below with reference to specific embodiments and with reference to certain drawings, but the invention is not limited thereto and is only limited by the appended claims. The described drawings are only schematic drawings that have no limiting character. In the drawings, the dimensions of certain elements may be exaggerated and may not be drawn to scale, all for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual practical applications of the invention.
    The following terms are provided only to aid in understanding the invention. • Maximum load capacity (Fm): the largest load that the steel fiber can withstand during a tensile test; • Elongation at maximum load (%): increase in measuring length of the steel fiber at maximum load, expressed as a percentage of the original measuring length; • Elongation at break (%): increase in measurement length at the time of breakage, expressed as a percentage of the original measurement length; • Tensile strength (Rm): voltage corresponding to the maximum load (Fm); • Tension: force divided by the original cross-sectional area of the steel fiber: • Dosage: amount of fibers added to a volume of concrete (expressed in kg / m3 or in% vol (1 vol% corresponds to 78.50 kg / m3)); • Concrete with normal strength: concrete with a strength that is less than or equal to the strength of concrete of the C50 / 60 classes as defined in EN206; • High-strength concrete: concrete with a strength greater than the strength of concrete of the C50 / 60 classes as defined in EN206.
    To illustrate the invention, a number of different steel fibers, both prior art steel fibers and steel fibers according to the present invention, are subjected to two different tests: a tensile test (stress-strain test); and a three-point bending test (load crack width curve or a load deflection curve) The tensile test is performed on the steel fiber, in particular on the center part of the steel fiber. Alternatively, the tensile test is performed on the wire used to produce the steel fibers.
    The tensile test is used to determine the maximum load capacity Fm of the steel fiber and to determine the elongation at the maximum load Ag + e.
    The three-point bending test is performed on a reinforced beam with a saw cut as specified in EN 14651.
    The test is used to determine the residual tensile strengths.
    The tests are illustrated in Figure 1 and Figure 2, respectively.
    Figure 1 is a representation of a test arrangement 60 for a tensile test (stress-strain test) of a steel fiber. Using the test arrangement 60, steel fibers are tested for the maximum load capacity Fm (breaking load), the tensile strength Rm, and the total elongation at the maximum load Ag + e.
    The anchoring ends (e.g. the enlarged or hook-shaped ends) of the steel fiber to be tested are first cut away. The remaining center part 14 of the steel fiber is fixed between two terminal pairs 62, 63. An increasing tensile force F is exerted on the center part 14 of the steel fiber via the terminals 62, 63. The displacement or elongation due to this increasing tensile force F is measured by measuring the displacement of the handles 64, 65 of the extensometer. L 1 is the length of the middle part of the steel fiber and is, for example, 50 mm, 60 mm, or 70 mm. 1_2 is the distance between the terminals and is, for example, 20 mm or 25 mm. L3 is the measuring length of the extensometer and is at least 10 mm, for example 12 mm, for example 15 mm. For an improved grip of the extensometer on the center portion 14 of the steel fiber, the center portion of the steel fiber can be coated or covered with a thin tape to prevent the extensometer from sliding over the steel fiber. A stress-strain curve is recorded by this test.
    The percentage of the total elongation at the maximum load is calculated using the following formula:
    Using the arrangement 60 of Figure 1, a number of different wires are tested for the maximum load capacity Fm (fracture load), the tensile strength Rm, and the total elongation at the maximum load Ag + e.
    Five tests per specimen were performed. Table 1 gives an overview of the tested wires.
    Table 1
    Low carbon steel is defined as being steel with a maximum carbon content of 0.15%, for example 0.12%; steel with an average carbon content is defined as being steel with a carbon content between 0.15% and 0.44%, for example 0.18%, and a steel with a high carbon content is defined as being with a carbon content greater than 0.44%, for example 0.5% or 0.6%.
    Figure 2 is a representation of the experimental set-up 200 for a three-point bend test. The three-point bending test is performed on 28 days, in accordance with the European Standard EN 14651, by using a 150 x 150 x 600 mm prismatic specimen 210. In the middle of the span of the specimen 210, a saw cut 212 with a depth of 25 mm applied by using a diamond saw blade to locate the crack. The arrangement comprises two supporting rollers 214, 216 and one load roller 218. The arrangement can be used in a controlled manner, that is, a constant displacement speed (CMOD or deflection) can be realized. The tests were performed with a displacement speed as specified in EN 14651. A load-crack width curve or a load-deflection curve is recorded.
    An example of a load-crack width curve 302 is shown in Figure 3.
    The residual bending tensile strengths fRj (fR, i and îr, 3) are determined in accordance with EN 14651, and can be calculated using the following expression:
    at which:
    Frj = the load corresponding to CMOD = CMODi or δ = δ Rj (1 = 1,2, 3,4) b = width of the specimen (mm) hsp = distance between the tip of the cut and the top of the specimen (mm ) L = span length of the specimen (mm) With the aid of the arrangement 200 according to figure 2, the performance of a number of different steel fibers (FIB1 to FIB5) in concrete is tested. For the test, the steel fibers were embedded in C35 / 45 concrete. The curing time was 28 days.
    An overview of the steel fibers that have been tested is shown in Table 2. The test results of the prior art steel fibers (FIB1 and FIB5) are shown in Table 3.
    The test results of the steel fibers according to the present invention (FIB2, FIB3, FIB4) are shown in Table 4.
    The steel fibers are specified by the length of the steel fiber, the wire type used to produce the steel fibers, the diameter of the steel fiber (more specifically the diameter of the middle part of the steel fiber), the number of straight sections of the anchoring end, the enclosed angle between the main axis of the middle section and the main axis of the first straight section, the orientation of the second straight section relative to the middle section, the enclosed angle between the main axis of the second straight section and the main axis of the third straight section, the orientation of the fourth straight section with respect to the center part, the included angle between the main axis of the fourth straight section and the main axis of the fifth straight section.
    The geometry of the different fibers is shown in Figures 4a to 4e.
    All the fibers 400 tested have anchoring ends 402 at both ends of the middle portion 404.
    Steel fibers FIB1 and FIB5 are steel fibers from the state of the art. The steel fiber FIB 1 is a low-carbon fiber with anchoring ends with two straight sections. Steel fiber FIB5 is a fiber that has a nail-shaped part at both ends as an anchoring end.
    The steel fibers FIB2, FIB3, FIB4 are fibers in accordance with the present invention. The steel fibers FIB2, FIB3, FIB4 are provided with anchoring ends with 3 straight sections (Figure 4b), 4 straight sections (Figure 4c) and 5 straight sections (Figure 4d).
    The steel fiber 400 as shown in Figure 4a is provided with a center portion 404 and with an anchor end 402 at both ends of the center portion 404. The center portion 404 has a major axis 403. Each of the anchor ends 402 has a first bent section 405, a first straight section 406, a second curved section 407, and a second straight section 408. The enclosed angle between the main axis 403 of the middle section 404 and the main axis of the first straight section 406 is indicated by a.
    The second straight section 408 is parallel or substantially parallel to the major axis 403 of the middle portion 404.
    The steel fiber 400 as shown in Fig. 4b includes a center portion 404 and an anchor end 402 at both ends of the center portion 404. The center portion 404 has a major axis 403. Each of the anchor ends 402 has a first bent section 405, a first straight section 406, a second curved section 407, a second straight section 408, a third curved section 409, and a third straight section 410. The enclosed angle between the main axis 403 of the middle part 404 and the main axis of the first straight section 406 is indicated by a. The enclosed angle between the major axis of the second straight section 408 and the major axis of the third straight section 410 is indicated by β.
    The second straight section 408 is parallel or substantially parallel to the major axis 403 of the middle portion 404.
    The steel fiber 400 as shown in Fig. 4c includes a center portion 404 and an anchor end 402 at both ends of the center portion 404. The center portion 404 has a major axis 403. Each of the anchor ends 402 has a first bent section 405, a first straight section 406, a second curved section 407, a second straight section 408, a third curved section 409, a third straight section 410, a fourth curved section 411, and a fourth straight section 412. The enclosed angle between the main axis 403 of the middle portion 404 and the major axis of the first straight section 406 is indicated by a. The enclosed angle between the major axis of the second straight section 408 and the major axis of the third straight section 410 is indicated by β.
    The second straight section 408 and the fourth straight section 412 are parallel or substantially parallel to the major axis 403 of the middle section 404.
    The steel fiber 400 as shown in Figure 4d includes a center portion 404 and an anchor end 402 at both ends of the center portion 404. The center portion has a major axis 403. Each of the anchor ends 402 has a first curved section 405, a first straight section 406, a second curved section 407, a second straight section 408, a third curved section 409, a third straight section 410, a fourth curved section 411, a fourth straight section 412, a fifth curved section 413, and a fifth straight section 414. The enclosed angle between the main axis 403 of the middle section 404 and the main axis of the first straight section 406 is indicated by a. The enclosed angle between the main axis of the second straight section 408 and the main axis of the third straight section 410 is indicated by ß. The enclosed angle between the major axis of the fourth straight section 412 and the major axis of the fifth straight section 414 is indicated by γ.
    The second straight section 408 and the fourth straight section 412 are parallel or substantially parallel to the major axis 403 of the middle section 404.
    The fiber shown in Fig. 4e comprises a middle part 404 which is provided with anchoring ends 402 at both ends of the middle part 404. The anchoring ends 402 comprise nail-head shaped parts.
    Table 2
    α = enclosed angle between the main axis of the middle section and the main axis of the first straight section β = enclosed angle between the main axis of the second straight section and the main axis of the third straight section Y = enclosed angle between the main axis of the fourth straight section and the major axis of the fifth straight section
    Table 3
    Table 4
    It can be deduced from Table 3 and Table 4 that the ratio fR, 3 / fR, i of the prior art fibers (FIB1 and FIB5) is less than 1, while the ratio fR, 3 / fR, i of the steel fibers of the present invention (FIB2, FIB3, FIB4) is greater than 1.
    The residual flexural tensile strengths îr, i, îr, 2, îr, 3 of the fibers of the prior art (FIB1 and FIB5) are low, i.e. they are considerably lower than the residual flexural tensile strengths îr, i, îr, 2, 3 of the fibers according to the invention (FIB2, FIB3, FIB4).
    When comparing the steel fibers according to the present invention (FIB2, FIB3, FIB4) when using a dosage of 40 kg / m3, with the prior art steel fibers (FIB1 and FIB5) when using from a dosage of 40 kg / m 3, it can be seen that the residual flexural tensile strengths r,,, rr, 2, fR, 3 of the steel fibers according to the present invention are significantly higher than those of the prior art fibers.
    The steel fiber FIB3 was tested in two different dosages: 20 kg / m3 and 40 kg / m3. Even when a fiber dosage of 20 kg / m 3 was used, the ratio of fRy to 1 is greater than 1. This indicates that such steel fibers behave like traditional reinforcement steel (stress-strain based instead of stress-crack width based) .
    If a comparison is made of the steel fibers FIB2, FIB3, and FIB4, it can be concluded that the residual flexural tensile strengths îr, i, fR, 2> îr, 3 increase as the number of straight sections increases from 3 to 4.
    Also the ratio îr, 3 / îr, i increases as the number of straight sections increases from 3 to 4.
    By increasing the number of straight sections from 4 to 5, the residual bending tensile strengths fR1, fRi2, rr, 3 and the ratio îr, 3 / îr, i do not increase further.
    It is surprising to find that steel fibers with anchoring ends with four straight sections have the best performance.
    When the steel fibers from Table 2 are subjected to a pull-out test to determine the anchoring force, the FIB3 steel fiber (with four straight sections) shows the best anchoring in concrete.
    By way of example, steel fibers according to the invention can be produced as follows.
    The base material is a wire with a diameter of, for example, 5.5 mm or 6.5 mm, and with a steel composition with a minimum carbon content of, for example, 0.50% by weight (wt%), for example greater than or equal to 0.60 wt%, with a manganese content that lies is between 0.20% by weight and 0.80% by weight, and with a silicon content between 0.10% and 0.40% by weight. The sulfur content is at most 0.04% by weight and the phosphorus content is at most 0.04% by weight.
    A typical steel composition comprises 0.725% carbon, 0.550% manganese, 0.250% silicon, 0.015% sulfur and 0.015% phosphorus.
    An alternative steel composition comprises 0.825% carbon, 0.520% manganese, 0.230% silicon, 0.008% sulfur, and 0.010% phosphorus.
    The wire is cold-drawn in a number of steps until the final diameter is between 0.20 mm and 1.20 mm.
    In order to give the steel fiber steel fiber its high elongation at the moment of breakage and at the maximum load, the wire thus drawn can be tempered, for example, by passing the wire through a high-frequency or medium-frequency induction coil, the length of which is adapted to the speed at which the wire is being moved. It was found that a thermal treatment at a temperature of about 300 ° C for a certain period of time resulted in a reduction of the tensile strength of about 10%, without increasing the elongation at break and the elongation at the maximum load. By slightly raising the temperature to above 400 ° C, an additional decrease in tensile strength was observed and at the same time an increase in elongation at the moment of breakage, and an increase in elongation at the maximum load.
    The wires may or may not be coated with a corrosion-resistant coating such as a zinc or a zinc alloy coating, in particular a zinc-aluminum coating or a zinc-aluminum-magnesium coating. Prior to drawing or during drawing, the wires can also be coated with a copper or copper alloy coating to facilitate the drawing operation.
    The tempered wires are then cut to the lengths appropriate for the steel fibers and the appropriate anchoring shape or thickening is applied at the ends of the steel fibers. Cutting and forming the hooks can also be performed in one and the same processing step by using adapted rollers.
    The steel fibers thus obtained may or may not be glued together in accordance with US-A-4,284,667.
    In addition or alternatively, the obtained steel fibers can be combined into a package, such as, for example, a chain package or a belt-shaped package. A chain package is described, for example, in the document EP-B1-1383634; while a belt-shaped package is described in the European patent application with application number 09150267 in the name of the present applicant.
    权利要求:
    Claims (15)
    [1]
    Conclusions
    A steel fiber for reinforcing concrete or mortar, wherein the steel fiber comprises a central part, as well as an anchoring end at one or both ends of the central part, wherein the central part is provided with a main axis, wherein the anchoring end is at least in the possession of a first, a second, and a third straight section, wherein the first straight section is connected to the middle section by a first curved section, the second straight section is connected to the first straight section by a second curved section, the third straight section is connected to the second straight section by a third curved section, each of the first, second, third straight sections having a major axis, characterized in that the first straight section deflects away from the major axis of the middle part, leaving an enclosed angle is defined between the major axis of the middle part and the major axis of the first straight section, in that the second straight section is substantially parallel s on the main axis of the middle part, and because the third straight section bends away from the main axis of the middle part, in the same direction as the first straight section bends away from the main axis of the middle part, thereby defining an enclosed angle between the main axis of the second straight section and the main axis of the third straight section, with the enclosed angle between the main axis of the middle part and the main axis of the first straight section, and the enclosed angle between the main axis of the second straight section and the main axis of the third straight section are located between 100 and 160 degrees.
    [2]
    Steel fiber according to claim 1, wherein the anchoring end is furthermore provided with a fourth straight section, the fourth straight section being connected to the third straight section by means of a fourth curved section.
    [3]
    Steel fiber according to claim 2, wherein the fourth straight section is in the possession of a main axis that is substantially parallel to the main axis of the middle part.
    [4]
    The steel fiber according to claim 2, wherein the angle between the major axis of the fourth straight section and the major axis of the middle section is between -60 and +60 degrees.
    [5]
    Steel fiber according to any one of the preceding claims, wherein the enclosed angle between the main axis of the middle part and the main axis of the first straight section, and the enclosed angle between the main axis of the second straight section and the main axis of the third straight section are the same or are essentially the same.
    [6]
    Steel fiber according to any one of the preceding claims, wherein the middle part of the steel fiber has a tensile strength Rm of at least 1000 MPa.
    [7]
    Steel fiber according to any one of the preceding claims, wherein the middle part has an elongation at the maximum load Ag + e of at least 2.5%.
    [8]
    A steel fiber according to any one of the preceding claims, wherein the steel fiber is in an annealed state.
    [9]
    A steel fiber according to any one of the preceding claims, wherein the central part of the steel fiber is provided with at least one flattened section.
    [10]
    A steel fiber according to any one of the preceding claims, wherein the middle part of the steel fiber has a diameter that is between 0.1 mm and 1.20 mm.
    [11]
    A steel fiber according to any one of the preceding claims, wherein the steel fiber has a ratio of the length to the diameter L / D which is between 40 and 100.
    [12]
    A concrete structure reinforced with steel fibers according to one or more of claims 1-11.
    [13]
    A concrete structure according to claim 12, wherein the ratio of the residual flexural tensile strength r, 3 divided by the residual flexural tensile strength rr, i (îr, 3 / îr, i) is greater than 1 at a dosage of steel fibers that is less than 1 vol% .
    [14]
    A concrete structure according to claim 12 or claim 13, wherein the residual flexural tensile strength r, 3 is greater than 5 MPa at a dosage of steel fibers that is less than 1 vol%.
    [15]
    Use of steel fibers according to one of claims 1 to 11 for structural applications.
    类似技术:
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    同族专利:
    公开号 | 公开日
    BR112013014980A2|2016-09-13|
    AU2011343409B2|2016-04-07|
    CN103261544B|2016-06-01|
    CA2818995C|2018-05-01|
    EP2652222B1|2017-07-26|
    EP2652222A2|2013-10-23|
    WO2012080323A2|2012-06-21|
    CO6741172A2|2013-08-30|
    PT2652222T|2017-09-26|
    ZA201303767B|2014-07-30|
    CN103261544A|2013-08-21|
    PE20140338A1|2014-03-09|
    DK2652222T3|2017-11-06|
    CL2013001692A1|2013-12-06|
    MX350131B|2017-08-28|
    BR112013014980B1|2020-05-26|
    US20130255540A1|2013-10-03|
    PL2652222T3|2018-01-31|
    SI2652222T1|2017-11-30|
    JP5809287B2|2015-11-10|
    KR20130129385A|2013-11-28|
    HUE034880T2|2018-03-28|
    MX2013006300A|2013-06-28|
    CA2818995A1|2012-06-21|
    JP2014507362A|2014-03-27|
    ES2639791T3|2017-10-30|
    EA201300706A1|2013-11-29|
    AU2011343409A1|2013-06-13|
    WO2012080323A3|2012-11-08|
    US9435122B2|2016-09-06|
    NO2652222T3|2017-12-23|
    EA024218B1|2016-08-31|
    CR20130291A|2013-09-11|
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    法律状态:
    2019-10-02| MM| Lapsed because of non-payment of the annual fee|Effective date: 20181231 |
    优先权:
    申请号 | 申请日 | 专利标题
    EP10195105|2010-12-15|
    EP101951051|2010-12-15|
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