Composite steel bars

Abstract

An improved shaped composite steel bar is disclosed.

Description

[0001] This application is a divisional application, with its parent application having application number 201980075104.X, application date of October 24, 2019, and invention title "Composite Steel Bar".

[0002] Cross-reference to related applications

[0003] This application claims priority and all benefits to U.S. Provisional Patent Application No. 62 / 769,231, filed November 19, 2018, which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates generally to reinforcing bars and more specifically to glass fiber reinforced polymer (GFRP) reinforcing bars. Background Technology

[0005] Reinforcing steel bars are commonly used to strengthen concrete structures such as roads, bridges, tunnels, airport runways, floors, and parking lots. In these structures, the steel bars are embedded in the concrete, where they mechanically and chemically bond with it. The outer surface of the steel bars is often reinforced to strengthen this bond. Concrete provides compressive strength (generally known as compressive property) and the steel bars provide tensile strength (tensile property).

[0006] Reinforcing steel products made from fiber and resin composites are known in the art, as disclosed, for example, in US 5,650,220, US 6,048,598, and US 6,221,295, which are incorporated herein by reference in their entirety. Such composite reinforcing steel products are superior to those made from steel. First and foremost, in some concrete environments, composite reinforcing materials do not corrode and deteriorate like steel. Because steel reinforcing steel corrodes, it loses strength and becomes less effective under tensile, compressive, bending, or shear loads. Furthermore, as the steel corrodes, it expands significantly and “splits” the surrounding concrete material, making the concrete less effective under compressive loads. Other advantages of composite reinforcing steel include its non-metallic (or non-magnetic) and non-conductive properties, its tensile strength being approximately 2-3 times that of steel reinforcing steel, while weighing only 1 / 4 the weight, and its coefficient of thermal expansion being more compatible with concrete or rock than that of steel reinforcing steel.

[0007] These composite reinforcing bars are often produced through a pultrusion process and have a linear or uniform shape. A typical pultrusion process involves drawing a bundle of reinforcing material (e.g., fibers or filaments) from a source, wetting and impregnating the fibers in an open tank by passing the reinforcing material through a resin bath (preferably with a thermosetting polymer resin), passing the resin-wetted and impregnated bundle of material through a forming die to align the fiber bundle and control its formation of a suitable cross-sectional structure, and curing the resin in the die while maintaining filament tension. Because the fibers travel integrally through the pultrusion process without being cut or shredded, the resulting product typically has extremely high tensile strength in the longitudinal direction (i.e., the direction in which the filaments are pulled). Summary of the Invention

[0008] An improved composite steel reinforcement structure is provided herein, wherein at least a portion of the steel reinforcement has a non-linear shape.

[0009] Compared with conventional GFRP steel bars, the improvements of this shaped composite steel bar may include, but are not limited to, one or more of the following: increased glass content, increased elastic modulus, and increased tensile strength.

[0010] In one exemplary embodiment, a composite reinforcing bar includes: a plurality of continuous fibers arranged parallel to each other to form an elongated element, the fibers being impregnated with a resin matrix; and a fiber bundle wound helically around the outer surface of the elongated element to form a plurality of adjacent coils, wherein the resin matrix is ​​cured to fix the fibers relative to each other, wherein the distance between each pair of adjacent coils in the plurality of first adjacent coils is x, wherein the distance between each pair of adjacent coils in the plurality of second adjacent coils is y, and wherein x > y.

[0011] In some exemplary embodiments, x is 1.0-1.5 inches. In some exemplary embodiments, y is 0.1-0.9 inches.

[0012] In some exemplary embodiments, the continuous fiber is glass fiber. In some exemplary embodiments, the average diameter of the continuous glass fiber is 13-35 μm. In some exemplary embodiments, the average diameter of the continuous glass fiber is 17-32 μm.

[0013] In some exemplary embodiments, the resin matrix is ​​a thermosetting resin. In some exemplary embodiments, the resin matrix is ​​selected from polyester resins, vinyl ester resins, polyurethane resins, epoxy resins, and combinations thereof.

[0014] In some exemplary embodiments, the fiber bundles are formed of glass.

[0015] In some exemplary embodiments, the composite reinforcing bar also includes an expanded material applied to the outer surface of the elongated element. In some exemplary embodiments, the expanded material is sand.

[0016] In some exemplary embodiments, the composite reinforcing bar further includes a bend that forms a first straight section and a second straight section, wherein the central axis of the first straight section and the central axis of the second straight section intersect each other at the bend to form an angle z, z > 5 degrees. In some exemplary embodiments, z > 45 degrees. In some exemplary embodiments, z ≥ 90 degrees.

[0017] In some exemplary embodiments, the elbow includes more second adjacent coils than first adjacent coils.

[0018] In some exemplary embodiments, the elbow includes a plurality of second adjacent coils more than the first straight section, and the elbow includes a plurality of second adjacent coils more than the second straight section.

[0019] In some exemplary embodiments, fiber bundles are wound helically around the outer surface of an elongated element, such that adjacent coils extend along the length of the elongated element to form t sets of different adjacent coils, wherein each set of u adjacent coils includes a plurality of first adjacent coils spaced x, wherein each set of v adjacent coils includes a plurality of second adjacent coils spaced y, wherein t = u + v, wherein x > y, wherein each pair in the u set is applied to the elongated element portion that retains a straight section, and wherein each pair in the v set is applied to the elongated element portion that is bent.

[0020] In some exemplary embodiments, the elongated element is formed by a pultrusion process. In some exemplary embodiments, the elongated element has a circular cross-section.

[0021] In one exemplary embodiment, a method of forming a composite reinforcing bar includes: providing a plurality of continuous fibers arranged parallel to each other to form an elongated element; impregnating the fibers with a resin matrix; spirally winding the fiber bundle around the outer surface of the elongated element to form a plurality of first adjacent coils, each pair of adjacent coils being spaced x apart; spirally winding the fiber bundle around the outer surface of the elongated element to form a plurality of second adjacent coils, each pair of adjacent coils being spaced y apart; and partially curing the resin matrix to fix the fibers relative to each other and to adhere the fiber bundle to the elongated element, wherein x > y.

[0022] In some exemplary embodiments, x is 1.0-1.5 inches. In some exemplary embodiments, y is 0.1-0.9 inches.

[0023] In some exemplary embodiments, the continuous fiber is glass fiber. In some exemplary embodiments, the average diameter of the continuous glass fiber is 13-35 μm. In some exemplary embodiments, the average diameter of the continuous glass fiber is 17-32 μm.

[0024] In some exemplary embodiments, the resin matrix is ​​a thermosetting resin. In some exemplary embodiments, the resin matrix is ​​selected from polyester resins, vinyl ester resins, polyurethane resins, epoxy resins, and combinations thereof.

[0025] In some exemplary embodiments, the fiber bundles are formed of glass.

[0026] In some exemplary embodiments, the method further includes applying an expanded material to the outer surface of the elongated element. In some exemplary embodiments, the expanded material is sand.

[0027] In some exemplary embodiments, the method further includes: shaping an elongated element to have a first straight segment portion and a second straight segment portion, wherein a curved portion separates the first straight segment portion and the second straight segment portion; and fully curing a resin matrix to form a composite reinforcing bar.

[0028] In some exemplary embodiments, the elongated element is shaped to have four straight segments and four curved segments.

[0029] In some exemplary embodiments, the central axis of the first straight segment and the central axis of the second straight segment intersect each other at the curved portion to form an angle z, where z > 5 degrees. In some exemplary embodiments, z > 45 degrees. In some exemplary embodiments, z ≥ 90 degrees.

[0030] In some exemplary embodiments, the curved portion includes more second adjacent coils than the first adjacent coils.

[0031] In some exemplary embodiments, the curved portion includes more second adjacent coils than the first straight segment portion and the curved portion includes more second adjacent coils than the second straight segment portion.

[0032] In some exemplary embodiments, the elongated element has a circular cross-section.

[0033] In some exemplary embodiments, the step of providing fibers arranged in parallel to each other includes pultruding the fibers through at least one die.

[0034] In some exemplary embodiments, the step of impregnating the fibers with a resin matrix includes pulling the fibers through a resin bath.

[0035] Numerous other aspects, advantages, and / or features of the general inventive concept of the present invention will become more apparent from the following detailed description of exemplary embodiments, the claims, and the accompanying drawings. Attached Figure Description

[0036] The general inventive concept, its embodiments, and advantages are described in more detail below with reference to the accompanying drawings by way of examples, wherein:

[0037] Figure 1 The flowchart illustrates a method for forming shaped composite steel bars according to an exemplary implementation.

[0038] Figure 2A and 2B A description of conventional composite steel reinforcement is provided. Figure 2A This is a longitudinal side view of the composite steel reinforcement. Figure 2B It is along Figure 2A A cross-sectional view of the composite reinforcement of line AA.

[0039] Figure 3 A description of conventional shaped composite steel bars is provided.

[0040] Figure 4 An improved composite steel bar according to an exemplary implementation is described.

[0041] Figure 5 Described by Figure 4 The shaped composite steel bars are formed from composite steel bars.

[0042] Figure 6 This is a table of cross-sectional area measurement data for three shaped composite steel bar samples.

[0043] Figure 7 Table of fiber weight fraction measurement data for three shaped composite steel bar samples.

[0044] Figure 8 This is a table of modulus measurement data for two shaped composite steel bar samples.

[0045] Figure 9 This is a table showing the tensile strength measurement data for two shaped composite steel bar samples. Detailed Implementation

[0046] While the general inventive concept of this invention can be implemented in many different forms, some of which are shown in the accompanying drawings and will be described in more detail below, these specific embodiments should be understood as exemplary illustrations of the principles of the general inventive concept. Therefore, the general inventive concept of this invention is not limited to the specific embodiments described herein.

[0047] The general inventive concept of this invention includes glass fiber reinforced polymer (GFRP) steel bars for reinforcing concrete and the like, as well as systems and methods for producing such composite steel bars. The structure of the composite steel bars of this invention imparts improved mechanical properties. Therefore, the following description of the general inventive concept of the invention and its exemplary embodiments will focus on the beneficial properties of the innovative structure and the resulting steel bars.

[0048] For reference Figure 1 This describes a general method 100 for forming a composite steel bar 200 (such as a GFRP steel bar) according to an exemplary embodiment. Figure 1 As shown, in step 102, multiple fiber bundles 202 (hereinafter referred to as "fibers") used to form the composite reinforcement are arranged parallel to each other. For example, this arrangement can be achieved by structural elements that position the individual fibers 202 relative to each other. The fibers 202 are typically under tension.

[0049] As shown in Figures 2A and 2B, the arrangement of fibers 202 forms a rope-like element (hereinafter referred to as "rope"). Figure 2B As shown, rope 204 has a relatively cylindrical shape. As is known in the prior art, each fiber 202 is made of multiple individual filaments (such as glass filaments).

[0050] Next, in step 104, rope 204 is impregnated with resin. Any suitable resin system can be applied. Proper impregnation of rope 204 ensures that the resin not only coats the exterior of rope 204 but also penetrates and contacts the internal fibers 202 of rope 204, filling the gaps between the fibers 202. In some exemplary embodiments, rope 204 is impregnated with resin by pulling rope 204 through a resin bath.

[0051] Subsequently, in step 106, the rope 204 is wound to hold the resin-impregnated fibers 202 together. Specifically, as... Figure 2A As shown, fiber bundle 206 is wound around the outer periphery of rope 204.

[0052] The rope 204 can be formed to any desired length. Figure 2A Arrow 208 indicates the direction of rope formation. The formation direction is parallel to the central (longitudinal) axis of rope 204. Fiber bundles 206 are applied to rope 204 in a helical manner (i.e. at an angle relative to the central axis of rope 204), wherein the distance between corresponding portions of adjacent loops is taken as the spacing P of fiber bundles 206.

[0053] In some exemplary embodiments, in step 108, an expanded material (such as sand) is applied to the outer surface of the rope 204. The expanded material is used to reinforce the composite steel bar 200 anchored in concrete.

[0054] Next, in step 110, the resin-impregnated rope 204 is controlled so that at least a portion of the rope 204 exhibits a non-linear shape. The rope 204 can be shaped in any suitable manner. For example, the rope 204 can be bent relative to a fixed component (such as an anvil). As another example, the rope 204 can be wound around a mandrel. As yet another example, the rope 204 can be wound around a rod extending perpendicular to the turntable.

[0055] Finally, the resin is cured in step 112. The resin is fully cured to form the composite steel bar 200. However, further processing of the composite steel bar is common, such as cutting the composite steel bar 200 into multiple segments. The complete curing of the composite steel bar 200 can be carried out in stages (e.g., including different heating elements, different locations) and can be carried out over a relatively long period of time (e.g., days or weeks).

[0056] like Figure 2A As shown, fiber bundles 206 are typically applied to rope 204 in a uniform manner (along the length of rope 204) such that the spacing P remains constant. The spacing P of the fiber bundles 206 is typically relatively large, such as 1 inch or more. Therefore, as described here, a uniform and / or wide spacing P can cause problems and / or degrade the performance of the formed composite reinforcement when rope 204 is formed.

[0057] For example, such as Figure 3 As shown, the rope 204 can be shaped into a circle, ellipse, or other closed profile 300 (hereinafter referred to as "shaped reinforcement"). Therefore, the shaped reinforcement 300 has four bent portions 302 and four straight portions 304. Each bent portion 302 is adjacent to (and between) a pair of straight portions 304. Similarly, each straight portion 304 is adjacent to ( and between) a pair of bent portions 302.

[0058] Due to the stress applied to the rope 204 during forming, the fibers 202 in the bent portion 302 are more likely to shift or break than the fibers 202 in the straight portion 304. This may indicate that the fiber bundle 206 is insufficient to cope with these stresses. As a result, the bent portion 302 of the formed steel bar 300 may exhibit bulges or similar features, affecting not only aesthetics but also the performance of the formed steel bar 300. For example, while the straight portion 304 of the formed steel bar 300 has a relatively uniform circular cross-section, the bent portion 302 of the formed steel bar 300 has a deformed cross-sectional portion (e.g., forming more ellipses than circles).

[0059] In view of the above, it is recommended that the formed composite steel bars avoid or mitigate these problems.

[0060] First, a composite steel bar 400 is formed (e.g., according to process 100). The composite steel bar 400 is formed by arranging multiple fiber bundles (hereinafter referred to as “fibers”) (not shown) in parallel relative to each other.

[0061] like Figure 4As shown, the fibers are arranged to form a rope-like element (hereinafter referred to as "rope"). Rope 404 has a relatively cylindrical shape. Each fiber is made of multiple individual filaments. In some exemplary embodiments, at least some of the filaments are glass. In some exemplary embodiments, all the filaments are glass. Any suitable glass composition can be used to form the filaments. In some exemplary embodiments, the glass filaments are made of E-CR glass, such as Owens Corning of Toledo, Ohio, under the trademark. Those for sale. In some exemplary embodiments, the diameter of the glass filament is 13-35 μm. In some exemplary embodiments, the diameter of the glass filament is 17-32 μm.

[0062] Next, rope 404 is impregnated with resin. Any suitable resin system can be used. In some exemplary embodiments, the resin is a thermosetting resin. In some exemplary embodiments, the resin is a polyester resin, vinyl ester resin, polyurethane resin, epoxy resin, or a blend thereof. Proper impregnation of rope 404 ensures that the resin not only coats the exterior of rope 404 but also penetrates and contacts the internal fibers of rope 404 and fills the gaps between the fibers. In some exemplary embodiments, rope 404 is impregnated with resin by pulling rope 404 through a resin bath.

[0063] Subsequently, the rope 404 is wound to hold the resin-impregnated fibers together. Specifically, as... Figure 4 As shown, a fiber bundle 406 is wound around the outer periphery of the rope 404. In some exemplary embodiments, the fiber bundle 406 is made of the same material as the fiber. In some exemplary embodiments, the fiber bundle 406 is made of a material different from the fiber.

[0064] It can make 404 rope into any desired length. Figure 4 Arrow 408 indicates the direction of rope formation. The formation direction is parallel to the central (longitudinal) axis of rope 404. Fiber bundles 406 are applied to rope 404 in a helical manner (i.e. at an angle relative to the central axis of rope 404), wherein the distance between corresponding portions of adjacent loops is taken as the spacing P of fiber bundles 406.

[0065] In some exemplary embodiments, an expanded material (such as sand) is applied to the outer surface of the rope 404. The expanded material is used to reinforce the composite steel bar 400 anchored in concrete.

[0066] Next, control the resin-impregnated rope 404 such that at least a portion of the rope 404 assumes a non-linear shape. The shaping of the rope 404 can be achieved in any suitable manner. For example, the rope 404 can be bent relative to a fixed member (such as an anvil). As another example, the rope 404 can be wound around a mandrel. As another example, the rope 404 can be wound around a rod axis extending perpendicular to the turntable.

[0067] Finally, cure the resin. The resin is fully cured to form the composite reinforcing bar 400. However, further processing of the composite reinforcing bar is common, such as cutting the composite reinforcing bar 400 into multiple segments. The full cure of the composite reinforcing bar 400 can be implemented in stages (e.g., including different heating elements, different positions), and can be implemented over a relatively long period of time (e.g., several days or weeks).

[0068] It has been found that the fiber bundles 406 are crucial for the integrity of the fiber arrangement that pre-cures to form the rope 404. More specifically, it has been found that carefully controlling the distribution of the fiber bundles along the rope 404 and / or the spacing of the fiber bundles 406 will result in improved processing properties and / or mechanical properties of the composite reinforcing bar, especially when the reinforcing bar is ultimately formed into a non-linear shape.

[0069] In one exemplary embodiment, as Figure 4 shown, the fiber bundles 406 are applied to the rope 404 in a non-uniform manner such that the spacing P varies along the length of the rope 404. For example, the fiber bundles 406 are applied to the first portion 412 of the rope 404 at a first spacing P1, while the fiber bundles 406 are applied to the second portion 414 of the rope 404 at a second spacing P2. This process is repeated for each subsequent repetition of the first and second portions. In some exemplary embodiments, the length of the first portion 412 is different from the length of the second portion 414.

[0070] Typically P2 < P1. Typically, the first portion 412 and the second portion 414 are directly adjacent to each other such that there is no gap (i.e., a portion of the rope 404 without any fiber bundles 406). In some exemplary embodiments, the first spacing P1 is 0.1 - 1.5 inches. In some exemplary embodiments, the second spacing P2 is 0.1 - 0.9 inches.

[0071] Thus, when the rope 404 is shaped, the spacing variation (i.e., P1 and P2) alleviates performance issues and / or performance degradation of the shaped composite reinforcing bar.

[0072] For example, as Figure 5As shown, the rope 404 can be shaped into a circle, ellipse, or other closed profile 500 (hereinafter referred to as "shaped reinforcement"). Therefore, the shaped reinforcement 500 has four bent portions 502 and four straight portions 504. Each bent portion 502 is adjacent to (and between) a pair of straight portions 504. Similarly, each straight portion 504 is adjacent to ( and between) a pair of bent portions 502.

[0073] In summary, the straight section 504 is linear, with a deviation of no more than 3 degrees from the central axis of the original (unshaped) rope 404. The curved section 502 is non-linear, with a curvature greater than 3 degrees from the central axis of the original (unshaped) rope 404.

[0074] Due to the stresses applied to the rope 404 during forming, the fibers in the curved portion 502 are more likely to shift or break than the fibers in the straight portion 504. However, using a smaller spacing (i.e., a second spacing P2) in the curved portion 502 allows the fiber bundles 406 to better resist these stresses. This is possible because each of the first portions 412 of the rope 404 corresponds to or overlaps with the straight portion 504 of the formed steel bar 500. Similarly, each of the second portions 414 of the rope 404 corresponds to or overlaps with the curved portion 502 of the formed steel bar 500.

[0075] Therefore, most of the fiber bundles 406 applied to the first portion 412 will terminate at the straight section 504 of the formed steel bar 500, while most of the fiber bundles 406 applied to the second portion 414 will terminate at the bent section 502 of the formed steel bar 500. In some exemplary embodiments, a small number of fiber bundles 406 applied to the second portion 414 will terminate at one or both straight sections 504 adjacent to the bent section 502, wherein most of the fiber bundles 406 terminate at the bent section 502. For example, as Figure 5 As shown, the fiber bundle 406 applied to the second portion 414 extends through the curved portion 502 and extends for a predetermined length L into each straight portion 504 adjacent to the curved portion 502. In some exemplary embodiments, the length L is 1-6 inches.

[0076] Therefore, the bent portion 502 of the formed composite steel bar 500 is less susceptible to damage (such as bulging) than that of conventional formed composite steel bars (such as steel bar 300). In addition, the cross-sectional shape of the formed steel bar 500 is more uniform than the cross-sectional shape typically achieved by conventional formed composite steel bars (such as steel bar 300).

[0077] In an alternative embodiment, fiber bundles 406 are applied uniformly to rope 404, but the spacing P is limited to less than 1 inch (e.g., 0.1-0.9 inches). As described above, because the spacing of the fiber bundles 406 in the bent portion 502 of the forming rebar 500 is smaller than that typically applied, the forming rope 404 is less likely to cause problems and inconsistencies in the forming rebar 500.

[0078] As described in this article, shaped composite reinforcing bars (e.g., shaped reinforcing bar 500) exhibit improved performance compared to conventional shaped composite reinforcing bars. See also Figure 6-9 Additionally, visual inspection reveals that the formed composite steel bars exhibit a more consistent / regular appearance.

[0079] Figure 6 Table 600 provides the cross-sectional area (in) of three types of shaped composite steel bar samples. 2 (1) Conventional shaped composite steel bars (i.e., "Gen I bent steel bars"), (2) test bent steel bars with filler, and (3) test bent steel bars without filler. The filler is an additive in the resin system that forms the partially composite steel bar. In this case, the filler is clay. The red dashed line indicates the maximum allowable cross-sectional area according to ASTM D7957.

[0080] Figure 7 Table 700 provides the fiber weight fraction (%) for three types of shaped composite rebar samples: (1) conventional shaped composite rebar (i.e., "Gen I bent rebar"), (2) test bent rebar with filler, and (3) test bent rebar without filler. In the case of GFRP rebar, the fiber weight fraction indicates how much glass (percentage) is in the composite rebar. The red dashed line indicates the minimum fiber weight fraction required to meet ASTM D7957.

[0081] Figure 8 Table 800 provides the modulus of elasticity (GPa) for two types of shaped composite steel bar samples: (1) conventional shaped composite steel bars (i.e., “Gen I bending steel bars”), and (2) test bending steel bars (without filler). The upper red dashed line indicates the minimum modulus required to meet the CASS 807 standard, while the lower red dashed line indicates the minimum modulus required to meet the ASTM D7957 standard.

[0082] Figure 9 Table 900 provides the tensile strength (MPa) of two types of shaped composite steel bar samples: (1) conventional shaped composite steel bar (i.e., “Gen I bending steel bar”), and (2) test bending steel bar (without filler). The red dashed line indicates the minimum tensile strength required to meet the ASTM D7957 standard.

[0083] It should be understood that the scope of the general inventive concept is not limited to the specific exemplary embodiments given and described herein. Based on the disclosure of this application, those skilled in the art will not only understand the general inventive concept of the invention and its accompanying advantages, but will also discover various changes and modifications to the disclosed methods and systems. Therefore, all changes and modifications, and all equivalents thereof, are sought herein to cover the substance and scope of the general inventive concept of the invention as set forth herein and in the claims.

Claims

1. A composite steel reinforcement, comprising: Multiple continuous fibers arranged parallel to each other to form elongated elements, the fibers being impregnated with a resin matrix; and Fiber bundles are wound in a spiral manner around the outer surface of the elongated element to form t sets of different adjacent coils. The cured resin matrix fixes the fibers relative to each other. Each of one or more u-groups of adjacent coils includes multiple first adjacent coils spaced x apart. Each of one or more groups of adjacent coils (v groups) includes multiple second adjacent coils spaced y apart. Where x is 1.0-1.5 inches, Where y is 0.1-0.9 inches, Where t = u + v, Where x > y, Each pair in group u is applied to the slender element portion that maintains the straight section, and Each pair in group v is applied to the slender part of the bent element.

2. The composite steel bar of claim 1, wherein the continuous fiber is glass fiber.

3. The composite steel bar of claim 2, wherein the average diameter of the continuous fibers is 13-35 µm.

4. The composite steel bar of claim 2, wherein the average diameter of the continuous fibers is 17-32 µm.

5. The composite steel bar of claim 1, wherein the resin matrix is ​​a thermosetting resin.

6. The composite steel bar of claim 1, wherein the resin matrix is ​​selected from polyester resin, vinyl ester resin, polyurethane resin, epoxy resin and combinations thereof.

7. The composite steel bar of claim 1, wherein the fiber bundles are formed of glass.

8. The composite steel bar of claim 1 further includes an expanded material applied to the outer surface of the elongated element.

9. The composite steel bar of claim 8, wherein the expanded material is sand.

10. The composite steel reinforcement of claim 1, wherein u ≥ 4.

11. The composite steel reinforcement of claim 1, wherein v ≥ 4.

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