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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 deflects from the main axis of the center section in a deflection section. The anchorage end comprises n curved sections, with n equal to or greater than 2. The invention further relates to a concrete structure reinforced with steel fibers according to the present invention, and to the use of such steel fibers for structural applications.
    公开号:BE1021496B1
    申请号:E2011/0717
    申请日:2011-12-13
    公开日:2015-12-03
    发明作者:Ann Lambrechts；Frederik Vervaecke
    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 two curved 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 are provided with anchoring ends with at least two curved 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 was reinforced with fibers and more specifically concrete that was strengthened by means of metal fibers.
    It is known in the 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. Fibers are also known in the 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. US 4,233,364 describes straight steel fibers which are provided with ends which are flattened and which are provided with a flange in a plane which is substantially perpendicular to the flattened ends.
    Steel fibers with flattened angular ends are known from 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 currently known fibers 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 from 0.5 vol% (40 kg / m3) and higher and not exceptionally up to 1.5 vol% (120 kg / m3), are used to achieve the necessary performance to the extreme limit state (ULS). These high dosages make it difficult to mix and apply the concrete reinforced with the 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 advantageously for structural applications, thus using steel fibers in low to medium dosages, typically 1 vol% steel fibers or 0.5 vol% 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, a steel fiber is provided for reinforcing concrete or mortar.
    The steel fiber comprises a straight middle part and an anchoring end at one or both ends of the middle part.
    The middle part has a main axis. The anchoring end deflects from the main axis of the middle part in a deflection section. The anchoring end is connected to the middle part through this deflection section.
    The anchoring end has n bent sections, with n equal to or greater than 2.
    When the steel fiber of the present invention is in a stable position on a horizontal surface, and is projected on this horizontal plane, the vertical projections in this horizontal plane of all n bent sections of an anchoring end are along one side of the vertical projection in this horizontal plane of the main axis of the middle part.
    The deflection section has a radius of curvature. In addition, each curved section of an anchoring end 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 (if present) has a third curvature radius, the nth curved section (if present has a nth radius of curvature.
    As specified above, an anchoring end of a steel fiber according to the present invention is provided with at least n curved sections, with n equal to or greater than 2. In particular embodiments, an anchoring end of a steel fiber according to the present invention can have more than two include curved. In principle, there is no limitation on the number of bent sections of a steel fiber according to the present invention. However, the most preferred embodiments have three curved sections, four curved sections, or five curved sections.
    Since the deflection section can also be considered as a curved section, the steel fiber according to the present invention has n + 1 curved sections per anchoring end: one deflection section and n curved sections. A steel fiber with two anchoring ends therefore has 2x (n + 1) bent sections.
    The deflection section connects the anchoring end to the middle part and causes the anchoring end to deflect from the main axis of the middle part of the steel fiber. By "bending away" is meant here the lateral turning away with respect to a straight line, i.e. the lateral turning away relative to the main axis of the middle part of the steel fiber.
    When a steel fiber according to the present invention is in a stable position on a horizontal surface, and is projected on this horizontal plane, all vertical projections in this horizontal plane of all n bent sections of an anchoring end are along one side of the vertical projection in this horizontal plane of the main axis of the middle part.
    When a steel fiber according to the present invention is in a stable position on a horizontal surface, preferably none of the vertical projections of the n curved sections on this horizontal plane are on the vertical projection of the main axis or on the vertical projection of a line extending from said main axis.
    This means that only the vertical projection on this horizontal surface of the deflection section is located at least partially in the vertical projection on the horizontal surface of the main axis.
    By "stable position" is meant the position in which the steel fiber remains when it is laid down on a horizontal surface.
    The radius of curvature of the deflection section or of the bent sections of an anchoring end is preferably between 0.1 mm and 5 mm, for example between 0.5 mm and 3 mm, and is for example 1 mm, 1.2 mm, or 2 mm.
    The curvature radii of the deflection section and of the various curved sections of an anchoring end 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 the curvature radii of any other curved sections (if any) may be the same or different.
    An example of a steel fiber according to the present invention comprises a steel fiber provided with one or two anchoring end (s), wherein the anchoring end or the anchoring ends are provided with two curved sections: a first curved section and a second curved section. The second curved section is connected to the first curved section. The anchoring end or anchoring ends is / are connected to the center part of the steel fiber through the deflection section.
    In a first example, the second curved section is immediately connected to the first curved section and the first curved section is immediately connected to the deflection section.
    An alternative example of a steel fiber according to the present invention comprises a steel fiber provided with one or two anchoring end (s), wherein the anchoring end or the anchoring ends are provided with two curved sections: a first curved section and a second curved section. The second curved section is connected to the first curved section by a straight section. The first curved section is connected to the deflection section by a straight section.
    The length of a straight section between two consecutive curved sections is preferably between 0.1 mm and 5 mm, and is, for example, equal to 0.5 mm or 2 mm. "Consecutive curved sections" means curved sections that follow one another.
    The lengths of the different straight sections between the deflection section and the first curved section of an anchoring end or between two consecutive curved sections can be selected independently of each other. This means that the different straight sections can have the same or different lengths.
    An example comprises a steel fiber with straight sections, where all straight sections have a length of 2 mm.
    For example, an alternative includes a steel fiber with a first straight section (i.e., the straight section between the deflection section and the first curved section of an anchoring end) with a length of 0.5 mm, a second straight section (i.e., the second curved section and the first curved section of an anchoring end) with a length of 2 mm.
    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 steel fiber. 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 from the main axis of the middle part of the steel fiber (symmetrical fibers).
    Alternatively, one anchor end may deflect (deflect) in a particular direction relative to the main axis of the center portion of the steel fiber, while the other anchor end flexes (deflect) in the opposite direction to the major axis of the center portion of the steel fiber (asymmetrical) fiber).
    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.
    Steel fibers that are provided with consecutive curved sections along opposite sides of the main axis of the middle part, or which are provided with consecutive curved sections, one of which is located on the main axis of the middle part, tend to coagulate during mixing. Coagulating the steel fibers gives rise to an inhomogeneous distribution of the steel fibers in the concrete.
    The steel fibers of the present invention function particularly well, both in use limit state (SLS) of a concrete or mortar structure, and in ultimate 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 art that increasing the amount of fibers in concrete has a positive influence on the performance of the concrete reinforced with fibers.
    A great advantage of the present invention is that a good performance is achieved in SLS and in ULS, and this 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 in SLS of concrete reinforced with fibers is the residual flexural tensile strength fRti. The residual flexural tensile strength is derived from the load at a predetermined crack width displacement (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 fR, i is determined at CMC = 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 îr, 3 becomes determined at CMOD3 = 2.5 mm (5r, 3 = 2.17 mm), the residual flexural tensile strength fR, 4 is determined at CMOD4 = 3.5 mm (δR, i = 3.02 mm).
    The residual bending tensile strength fR, i is the most important requirement for SLS design.
    The residual flexural tensile strength fR3 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 art - the ratio between the residual flexural tensile strength fR, 3 and the residual flexural tensile strength fR, i (îr, 3 / îr, i) is high, even when low or moderate doses of steel fibers are used, such as, for example, doses smaller than 1 vol% or doses smaller 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 that are less than 0.5 vol%, for example 0.25 vol%.
    For concrete reinforced with steel fibers according to the present invention at a dosage of 0.5 vol%, and where use is made of a C35 / 45 concrete, the residual flexural tensile strength fRi3 is preferably greater than 3.5 MPa, greater than 5 MPa, or even larger than 6 MPa, for example 7 MPa.
    Fibers known from the prior art, such as, for example, steel fibers with conically shaped ends (nail heads), produced from low-carbon steel, work very well for limiting cracks to about 0.5 mm (SLS). However, these fibers exhibit low performance in ULS. This type of steel fiber breaks at crack width displacements that are smaller than those required for ULS.
    The ratio fRj3 / fRi1 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 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 fibers, the ratio fR, 3 / fR, 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 higher 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 center part of the steel fiber, has an elongation at the 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 an elongation at the maximum load, 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 the 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 the maximum load, Ag + e, is the sum of the plastic elongation at maximum load Ag, and of the elastic elongation.
    The elongation at the maximum load does not include the structural elongation As that can be caused by the wavy character of the central part of steel fiber (if present). In the case of a corrugated 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 achieved 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 manufactured. 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 the 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 fibers 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 the 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 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 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 an elongation at maximum load Ag + e of at least 1.5%, a tensile strength Rm of at least 1500 MPa and an elongation at maximum load Ag + e 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 middle 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, better 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 typically exhibits a ratio of the length to the diameter L / D that 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 fR, 3 and the residual flexural tensile strength fR, i (fR, 3 / fR, 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 fR, 3 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, use 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 uses moderate dosages of strong fibers in high-strength concrete.
    According to a third aspect, the use of steel fibers according to the present invention is provided for structural applications, that is, 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 4, 5, 6, and 7 are illustrations of a number of different embodiments of steel fibers according to the present invention;
    8 and 9 are illustrations of a number of different steel fibers provided with anchoring ends that do not meet the requirements of the present invention;
    10a, 10b, 10c, 10d and 10e are illustrations of a number of additional embodiments of steel fibers according to the present invention, and of a number of prior art steel fibers.
    Means of Carrying Out 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 not drawn to scale 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 break, 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-tear-width curve or a load-deflection curve). The tensile test is performed on the steel fiber, more particularly 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 (fracture 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 fibers 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 with a carbon content between 0.15% and 0.44%, for example 0.18%, and 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 shows the experimental set-up 200 of a three-point bend test. The three-point bending test is performed on 28 days, in accordance with the European Standard EN 14651, and 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, i.e. a constant displacement speed (CMOD or deflection) can be realized. The tests were performed at 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 îrj (îr, i and fRi3) are determined in accordance with EN 14651 and can be calculated using the following expression:
    at which:
    Frj = the load corresponding to CMOD = CMOD-ι or δ = δ Rii (i = 1,2, 3,4) b = width of the specimen (mm) hsp = distance between the point of the cut and the top of the saw specimen (mm) L = span length of the specimen (mm) A number of embodiments of the steel fibers according to the present invention are described below.
    A first steel fiber 400 is shown in Figure 4. Steel fiber 400 is provided with a middle part 402 and two anchoring ends 406, 408, one at each end of the middle part 402. The middle part 402 has a main axis 404. The anchoring ends 406, 408 bend away from the main shaft 404 in a deflection section 410. In the embodiment shown in Figure 4, both anchoring ends of the main shaft 404 of the middle part 402 bend away in the same direction. However, it will be apparent to those skilled in the art that embodiments may also be taken into consideration with anchor ends bending away in different directions.
    Both anchoring ends 406, 408 have two curved sections: a first curved section 420 and a second curved section 422. The first curved section 420 is connected to the deflection section 410 by a first straight section 412; the second curved section 422 is connected to the first curved section by a second straight section 414. The anchoring ends 406, 408 are furthermore provided with a third straight section 416 which is connected to the second curved section 422.
    The second straight section 414 bends away in the curved section 420 in the direction of the main axis 404 of the middle portion 402; the third straight section 416 bends away from the main axis 404 of the middle portion 402 in the curved section 422.
    When the steel fiber 400 is in a stable position on a horizontal surface, and is projected vertically on this horizontal surface, the vertical projections of the first curved section 420 and of the second curved section 422 are along one side of the vertical projection. this horizontal surface of the main axis 404 of the middle part 402 of the steel fiber 400.
    None of the vertical projections of the first curved section 420 and of the second curved section 422 is located on the vertical projection of the main axis 404 of the middle portion 402 of the steel fiber 400.
    A second embodiment of steel fiber 500 according to the present invention is shown in Figure 5. The steel fiber 500 is provided with a middle part 502 with a main axis 504. The steel fiber 500 has two anchoring ends 506, 508, one at each end of the middle part 502. Both anchoring ends 506, 508 bend away from the main shaft 504 in the deflection section 510. In the embodiment shown in Figure 5, both anchoring ends bend away from the main shaft 504 of the middle part 502 in the opposite direction.
    Both anchoring ends 506, 508 have three curved sections: a first curved section 520, a second curved section 522, and a third curved section 524. The first curved section 520 is connected to the deflection section 51 by a first straight section 512; the second curved section 522 is connected to the first curved section 520 by means of a second straight section 514; the third curved section 524 is connected to the second curved section 522 by means of a third straight section 516. The anchoring ends 506, 508 also have a fourth straight section 418 which is connected to the third curved section 524.
    The second straight section 514, the third straight section 516, and the fourth straight section all flex away from the main axis 504 of the middle portion 502, respectively in the first curved section 520, the second curved section 522, and the third curved section 524.
    When the steel fiber 500 is in a stable position on a horizontal surface, and is projected vertically on this horizontal surface, the vertical projections of the first curved section 520, of the second curved section 522, and of the third curved section 524 are along one side of the vertical projection on this horizontal surface of the main axis 504 of the middle portion 502 of the steel fiber 500.
    None of the vertical projections of the first curved section 520, of the second curved section 522, or of the third curved section is located on the vertical projection of the main axis 504 of the middle portion 502 of the steel fibers 500.
    A third embodiment of the steel fiber 600 according to the present invention is shown in Figure 6. The steel fiber 600 has a central part 602 with a main axis 604. The steel fibers 600 are provided with two anchoring ends 606, 608, one at each end of the center part 602. Both anchoring ends 606, 608 bend away from the main shaft 604 in the deflection section 610. In the embodiment shown in Figure 6, both anchoring ends bend away in opposite directions from the main shaft 604 of the middle part 602. Both anchoring ends 606 608 have two curved sections: a first curved section 620 a second curved section 622. The first curved section 620 is connected to the deflection section 610 by means of a first straight section 612; the second curved section 622 is connected to the first curved section 620 by means of a second straight section 614. The anchoring ends 606, 608 are furthermore provided with a third straight section 616 which is connected to the second curved section 622.
    The second straight section 614 is oriented parallel or substantially parallel to the main axis 604 of the middle part 602. The third straight section 624 bends away from the main axis 604 of the middle part 602 in curved section 622.
    When the steel fiber 600 is in a stable position on a horizontal surface, and is projected vertically on this horizontal surface, the vertical projections of the first curved section 620 and of the second curved section 622 are located along one side of the vertical projection on this horizontal surface of the main axis 604 of the middle portion 602 of the steel fiber 600.
    None of the vertical projections of the first curved section 620 or of a second curved section 622 are located on the vertical projection of the main axis 604 of the middle portion 602 of the steel fibers 600.
    Figure 7 is a representation of an additional embodiment of a steel fiber 700 according to the present invention. The steel fiber 700 is provided with two anchoring ends 706, 708, one at each end of the middle part 702.
    Both anchoring ends bend away from the main shaft 704 in deflection section 710.
    Both anchoring ends 706, 708 have two curved sections: a first curved section 712 and a second curved section 714. The first curved section 712 is directly connected to the deflection section 710; the second curved section 714 is directly connected to curved section 712.
    When the steel fiber 700 is in a stable position on a horizontal surface, and is projected vertically on this horizontal surface, the vertical projections on this horizontal surface of the first curved section 712 and of the second curved section 714 are located along one side of the vertical projection on this horizontal surface of the main axis 704 of the central portion of the steel fiber 700.
    Figure 8 and Figure 9 are views of two embodiments of steel fibers that do not meet the requirements of the present invention.
    Figure 8 is a representation of a steel fiber 800 with a central portion 802 with a major axis 804. The steel fiber 800 has two anchoring ends 806, 808, one at each end of the central portion 802. Both anchoring ends 806, 808 are connected to the central portion by deflection section 810 The anchoring ends 806, 808 comprise three straight sections: a first straight section 812, a second straight section 814, and a third straight section 816. The anchoring ends 806, 808 comprise two curved sections: a first curved section 820 and a second curved section 822.
    When the steel fiber 800 is in a stable position on a horizontal surface, and is projected vertically on this horizontal surface, the vertical projections on this horizontal surface of curved section 820 and of curved section 822 are located on opposite sides of the vertical projection of the main axis 804 of the middle part 802 of steel fiber 800.
    A disadvantage of this type of steel fiber is that these fibers tend to coagulate during mixing. The steel fibers interlock and form balls during mixing.
    The result is that the steel fibers are not homogeneously distributed in the concrete or in the mortar.
    Figure 9 is a representation of a steel fiber 900 with a middle part 902 with a main axis 904. The steel fiber has two anchoring ends 906, 908, one at each end of the middle part 902. Both anchoring ends 806, 808 are connected to the middle part 902 by a curved section (deflection section) 910. The anchoring ends 806, 808 comprise two curved sections: a first curved section 912 and a second curved section 914.
    First curved section 912 is directly connected to deflection section 910.
    When the steel fiber 900 is in a stable position on a horizontal surface, and is projected vertically on this horizontal surface, the vertical projection on this horizontal surface of curved section 912 is located along one side of the vertical projection of the main axis 904 of the middle part 902 made of steel fiber 900.
    The vertical projection on this horizontal surface of curved section 914 is located on the vertical projection of the main axis 904 of the central portion 902 of steel fiber 900.
    A disadvantage of this type of steel fibers is that these fibers tend to coagulate during mixing. The steel fibers interlock and form balls during mixing.
    The result is that the steel fibers are not homogeneously distributed in the concrete or in the mortar.
    The performance of a number of different steel fibers (FIB1 to FIB5) in concrete is tested with the aid of the arrangement 200 from figure. For the test, the fibers are embedded in C35 / 45 concrete. The curing time was 28 days.
    An overview of steel fibers that were tested can be found in table 2. The test results of steel fibers according to the state of the art (FIB1 and FIB5) can be found in table 3. The test results of the steel fibers according to the invention (FIB2, FIB3, FIB4) can be found in table 4.
    The steel fibers are characterized by the length of the steel fibers, the type of wire from which the steel fibers are produced, 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 part and the main axis of the first straight section, the orientation of the second straight section relative to the middle part, 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 series section.
    The geometry of the different fibers is shown in Figures 10a to 10e.
    All fibers 1000 tested are provided with anchoring ends 1002 at both ends of the middle portion 1004. FIB1 and FIB5 are prior art fibers. FIB1 is a low carbon steel fiber with anchoring ends with two straight sections (Figure 10a). FIB5 is a fiber that is provided with a nail head as an anchoring end at both ends (figure 10e). FIB2, FIB3, FIB4 are fibers according to the present invention. FIB2 is provided with anchoring ends with 3 curved sections and 3 straight sections (figure 10b). FIB3 is provided with anchoring ends with 4 curved sections and 4 straight sections (figure 10c). FIB4 is provided with anchoring ends with 5 curved sections and 5 straight sections (figure 10d).
    By the term "enclosed angle" is meant the angle made by two straight sections with a common intersection. This means that the included angle between the main axis of the middle part and the main axis of the first straight section is defined as the angle made 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 formed by the major axis of the second straight section and the major axis of the third straight section.
    The steel fiber 1003 shown in Figure 10a includes a center portion 1004 and an anchor end 1002 at both ends of the center portion 1004. The center portion 1004 has a major axis 1003. The anchor ends 1002 deflect in deflection section 1005. Each of anchor ends 1002 includes a first straight section 1006, a first curved section 1007 and a second straight section 1008. The enclosed angle between the main axis 1003 of the middle portion 1004 and the major axis of the first straight section 1006 is indicated by α
    The second straight section 1008 is parallel or substantially parallel to the major axis 1003 of the middle portion 1004.
    The steel fiber 1000, which can be found in Figure 10b, comprises a middle part 1004 and an anchoring end 1002 at both ends of the middle part 1004. The middle part is provided with a main axis 1003. Each of the anchoring ends 1002 deflects from the main axis 1003 of the middle portion 1004 in deflection section 1005. The anchoring ends include a first straight section 1006, a first curved section 1007, a second straight section 1008, a second curved section 1009, and a third straight section 1010. The enclosed angle between the main axis 1003 of the middle portion 1004 and the major axis of the first straight section 1006 is indicated by a. The enclosed angle between the major axis of the second straight section 1008 and the major axis of the third straight section 1010 is indicated by β.
    The second straight section 1008 is parallel or substantially parallel to the major axis 1003 of the middle portion 1004.
    The steel fiber 1000, which can be found in Figure 10c, comprises a middle part 1004 and an anchoring end 1002 at both ends of the middle part 1004. The middle part 1004 has a main axis 1003. The anchoring ends 1002 deflect from the main axis 1003 of the center part 1004 in the deflection section 1005. Each of the anchoring ends 1002 has a first straight section 1006, a first curved section 1007, a second straight section 1008, a second curved section 1009, a third straight section 1010, a third curved section 1011, and a fourth straight section 1012. The enclosed angle between the main axis 1003 of the middle part 1004 and the main axis of the first straight section 1006 is indicated by a. The enclosed angle between the main axis of the second straight section 1008 and the main axis of the third right-hand section 1010 is indicated by ß.
    The second straight section 1008 and the fourth straight section are parallel or substantially parallel to the major axis 1003 of the middle portion 1004.
    The steel fiber 1000 reflected in Fig. 10d includes a center portion 1004 and an anchor end 1002 at both ends of the center portion 1004. The center portion has a major axis 1003. Each of the anchor ends 1002 deflects from the major axis 1003 of the middle part 1004 in deflection section 1005. The anchoring ends 1002 comprise a first straight section 1006, a first curved section 1007, a second straight section 1008, a second curved section 1009, a third straight section 1010, a third curved section 1011, a fourth straight section section 1012, a fourth curved section 1013, and a fifth straight section 1014. The enclosed angle between the main axis 1003 of the middle part 1004 and the main axis of the first straight section 1006 is indicated by a. The enclosed angle between the main axis of the second straight section 1008 and the major axis of the third straight section 1010 are indicated by ß. The enclosed angle between the major axis of the fourth section 1012 and the major axis of the fifth section 1014 is indicated by γ.
    The second straight section 1008 and the fourth straight section 1012 are parallel or substantially parallel to the major axis 1003 of the middle portion 1004.
    The fiber reflected in Fig. 10e comprises a middle part 1004 which is provided with anchoring ends 1002 at both ends of the middle part 1004. The anchoring ends 1002 comprise nail heads.
    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 fru / ffu ratio of the prior art fibers (FIB1 and FIB5) is less than 1, while the ≤3.3 / ≤1 ratio of the steel fibers according to the present invention (FIB2, FIB3, FIB4) is greater than 1.
    The residual flexural tensile strengths îr, i, îr, 2, îr, 3 of the fibers from the prior art (FIB1 and FIB5) are low, i.e. considerably lower than the residual flexural tensile strengths fR, i, fR, 2, îr, 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 is seen that the residual flexural tensile strengths fR, i, fR, 21 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 / m3 was used, the ratio fR, 3 / fR, i is greater than 1. This indicates that such steel fibers behave like traditional reinforcement steel (stress-strain based instead of stress-crack width based ).
    When comparing the steel fibers FIB2, FIB3, and FIB4, one can conclude that the residual flexural tensile strengths fR, i, fR, 2, fR, 3 increase as the number of straight sections increases from 3 to 4.
    Also the ratio fR, 3 / fRii increases when 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 fR, i, fR2, fru and the ratio fR, 3 / r, 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 steel fiber FIB3 (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 between 0.20% and 0.80%, and with a silicon content between 0.10% and 0.40%. 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 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 moved is becoming. 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 the tensile strength was observed and at the same time an increase in the elongation at the time of the break and an increase in the 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 (12)
    [1]
    Conclusions
    A steel fiber for reinforcing concrete or mortar, wherein said steel fiber comprises a straight middle part and an anchoring end at one or both ends of said middle part, wherein the middle part is provided with a main axis, the anchoring end being connected to the middle part by a deflection section, wherein the anchoring end deflects from the main axis of the center part in this deflection section, the anchoring end comprising n curved sections, with n equal to or greater than 2, said steel fiber when in a stable position on a horizontal surface, wherein a vertical projection is defined on said horizontal surface, and when a vertical projection is performed on said horizontal surface, the vertical projections of all n curved sections of the anchoring end are along one side of the vertical projection of the said main axis.
    [2]
    The steel fiber according to claim 1, wherein, in the vertical projection on the horizontal surface, the vertical projection of none of said n bent sections is located on the vertical projection of said main axis or on the vertical projection of a line extending extends from said main axis.
    [3]
    3. Steel fiber according to any one of the preceding claims, wherein said middle part of the steel fiber has a tensile strength R m of at least 1000 MPa.
    [4]
    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%.
    [5]
    Steel fiber according to one of the preceding claims, wherein the steel fiber is in an annealed state.
    [6]
    6. Steel fiber according to one of the preceding claims, wherein the middle part of the steel fiber is provided with at least one flattened section.
    [7]
    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.
    [8]
    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.
    [9]
    Concrete structure reinforced with steel fibers according to one or more of claims 1-7.
    [10]
    The concrete structure of claim 13, wherein the residual flexural tensile strength fR, 3 divided by the residual flexural tensile strength fRti (fR, 3 / fpu) is greater than 1 at a dosage to said steel fibers of less than 1 vol%.
    [11]
    A concrete structure according to claim 13 or claim 14, wherein the residual flexural tensile strength fR, 3 is greater than 5 or even greater than 6, at a dosage to said steel fibers that is less than 1 vol%.
    [12]
    The use of steel fibers according to any one of claims 1-8 for structural applications.
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    同族专利:
    公开号 | 公开日
    PT2652221T|2017-10-05|
    HUE037083T2|2018-08-28|
    PL2652221T3|2018-01-31|
    AU2011343412A1|2013-06-13|
    CO6741171A2|2013-08-30|
    JP2014506223A|2014-03-13|
    US20130269572A1|2013-10-17|
    JP5881731B2|2016-03-09|
    EA201300703A1|2013-11-29|
    EA025712B1|2017-01-30|
    WO2012080326A3|2012-11-15|
    AU2011343412B2|2016-04-14|
    CA2819219A1|2012-06-21|
    MX2013006769A|2013-07-22|
    WO2012080326A2|2012-06-21|
    CR20130290A|2013-09-12|
    US8962150B2|2015-02-24|
    PE20140369A1|2014-03-12|
    ZA201303799B|2014-07-30|
    BR112013015232A2|2016-09-13|
    CN103261542A|2013-08-21|
    CA2819219C|2018-06-05|
    KR20140003439A|2014-01-09|
    BR112013015232B1|2020-05-26|
    EP2652221B1|2017-08-16|
    CL2013001690A1|2013-12-06|
    ES2641065T3|2017-11-07|
    EP2652221A2|2013-10-23|
    SI2652221T1|2017-12-29|
    DK2652221T3|2017-11-20|
    NO2652221T3|2018-01-13|
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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
    EP10195107|2010-12-15|
    EP101951077|2011-12-13|
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