JP3833658B2 - Coated PC steel strand - Google Patents

Description

  The present invention relates to a PC steel stranded wire having a resin coating. In particular, the present invention relates to a coated PC steel stranded wire that has good adhesion to the grout and has low friction against a plastic or metal sheath.

  An anchor structure used for reinforcing the slope is shown in FIG. This anchor structure is made by inserting a PC steel stranded wire 111 into a drilling hole 110 formed by boring on a slope, a fixing length part around which a PC steel stranded wire is fixed with a grout 112, and a PC steel stranded wire. And a free length part of which is covered with a sheath. The slope is provided with a pedestal 113 and a bearing plate 114, and the ends of the twisted PC steel wire are fixed with a fixing tool 115.

  In such an anchor structure, the adhesion property between the wire and the grout of the PC steel of the fixing length is important. If the adhesion characteristics are poor, there may be a problem that the wire pulls out from the PC steel if the load applied to the wire from the PC steel increases during tension work of the PC steel after grout hardening or due to ground changes.

  As a countermeasure, the anchor fixing length can be lengthened, that is, the contact area of the PC steel wire with the grout can be increased (prevention of pull-out). However, for that purpose, it is necessary to increase the length of the drilling hole, and the influence on the construction cost increase is inevitable.

  In addition, when a wire is tensioned from PC steel, a plastic sheath is often used in order to secure a space that freely extends at the free length. Since the specific gravity of the boring occupying the construction cost is high, the diameter of the drilling hole is often reduced, and a sheath having a small diameter is inevitably used. In this case, the contact between the wire and the sheath is greater than that of the PC steel, and when the friction with the sheath is large, the necessary anchor force is not transmitted to the ground. Therefore, it is desirable that the friction between the PC steel strand and the sheath be as small as possible.

  On the other hand, in the PC cable used for the bridge, the relationship between the adhesion with the grout and the friction characteristic with the sheath becomes a problem. As an example in which a PC cable is used for a bridge, as shown in FIG. 13, a bridge having a so-called inner cable structure can be cited. This is because a sheath 121 is arranged in a bridge girder 120, a plurality of PC steel strands 122 are inserted into the sheath, and the PC steel strand 122 is tensioned and fixed, and the PC steel strand 122 and the sheath 121 are arranged. In this structure, grout 123 is filled in between.

  Even in this structure, if the adhesion between the wire from the PC steel and the grout injected into the sheath is poor, the fracture strength as a PC structural member is reduced.

  Also, when inserting a strand of PC steel into the sheath or tensioning the strand of PC steel, it is desirable that the friction between the sheath and the wire is smaller than that of the PC steel in order to transmit the largest possible load to the fixing side. On the other hand, in order for a PC structure or anchor to perform its function over a long period of time, it is necessary to ensure the durability of the strands of PC steel constituting the cable used.

  For this reason, various types of anticorrosion cables have been developed recently, but in particular, many of the wires coated with plastic on the surface of bare PC steel have been developed. PC steel strands coated with these plastics have a coating thickness of about 0.3 to 1.0 mm in order to ensure the necessary corrosion resistance. Therefore, it is often structured so that the eyes are not clearly covered with the coated surface of the bare PC steel, and the adhesion characteristics with the grout is similar to that of the bare PC steel due to the problem of the surface properties of the plastic. Compared to lower. Therefore, by applying various processing to the surface of the wire from the coated PC steel, the adhesion characteristics with the grout are enhanced.

These methods include the following methods.
Prior Art 1: An epoxy resin, a thermosetting resin, is coated to a thickness of 0.25 to 1.3 mm so that the strands of the PC steel are more visible. Sandy particles having a size of about 75 to 200 μm are embedded so as to be partially exposed from the surface (Patent Document 1).
Prior art 2: A plastic coating layer is formed so that the strands of the strands of the strands of PC steel appear on the outer surface, and the surface is roughened by numerous irregularities by shot blasting or the like (Patent Document 2).

  Prior art 3: Concavities and convexities are formed on a rough surface layer of an aggregated polyolefin resin emulsion that is familiar with the coating layer on the coating layer of the PC steel strand coated with the thermoplastic resin (Patent Document 3).

  Prior art 4: PC steel stranded wire coated with thermoplastic resin, which has a large number of small ridges that are continuous on the outer periphery of the coating layer, or helical ridges (Patent Document 4, Patent Document) 5, Patent Document 6).

  Prior art 5: Powder coating layer made of inorganic powder (hydraulic cement, gypsum powder, silica powder, etc. with a particle size of 50 μm or less) on the outer periphery of a rust-proof coating layer of PC steel wire coated with thermoplastic resin Are integrally formed, and the inorganic powder becomes pasty and solidified by grout or the like (Patent Document 7).

Japanese Patent Publication No. 3-28551 JP-A-5-1111912 JP-A-8-170405 JP-A-8-42062 Japanese Patent No. 2909470 Japanese Patent No.2761522 Japanese Patent No. 2761523

  However, these coated PC steel strands have a problem that none of the properties of both the adhesion to the grout and the frictional property with the sheath are equal to or higher than those of the bare PC steel.

  (1) In the prior art 1, the resin surface is devised focusing only on the adhesion characteristics. The hard epoxy resin is firmly attached to the wire than the PC steel, and a relatively large granular material of about 75 to 200 μm is embedded on the resin surface, so the adhesion characteristics are much larger than the wire of the bare PC steel It will be a thing. However, this causes a problem that the friction with the sheath is considerably increased.

  Because of the large friction, it takes time to insert the wire from the coated PC steel into the sheath. In addition, when the plastic sheath is used, the inner surface of the sheath is scraped and the granular material itself falls off. And if the friction is large, it becomes uneconomical because it is necessary to increase the number of wires from the coated PC steel in order to secure the prestressing force or anchoring force.

  Also, when a wire is drawn from the coated PC steel from the coil, the coating resin is rubbed and the film thickness is reduced.

  (2) Prior art 2 improves the adhesion characteristics with grout by making the surface of the skin rough, which gives minute dents to the plastic surface. However, when continuously produced, the shot is worn, resin debris is mixed in the shot, and the dent is often rounded. For this reason, it may be difficult to form a minute dent that ensures an adhesive force in continuous production. Further, if the sheath to be inserted is made of plastic, the plastic comes into contact with each other, which may increase friction.

  (3) In the prior art 3, an emulsion layer of polyolefin resin containing aggregate is provided on the surface of the coating resin, but the surface of the aggregate is covered with the emulsion and may be rounded. As a result, the adhesion properties with the grout can be significantly reduced.

  (4) Prior art 4 is a technique in which the shape of the thermoplastic coating surface is changed. That is, although the surface is provided with pleated irregularities, even if the grout enters these gaps, the crease is relatively easily deformed, so the adhesion characteristics with the grout are not greatly improved.

  (5) Prior art 5 provides a powder deposit layer made of inorganic powder on the surface of the anti-corrosion coating layer, and when the wire is embedded from the coated PC steel in the hydraulic concrete, the inorganic powder becomes a paste. Adhesive properties can be obtained by solidification. The powder coating layer is formed by extruding the die and pressing it onto the surface of the anticorrosive coating layer. Therefore, almost no irregularities can be expected on the surface of the powder coating layer, and when the inorganic powder is embedded in the rust-proof coating layer, the effect of improving the adhesion characteristics is small and the adhesion characteristics are unstable.

  (6) In the prior arts 3 to 5, the resin to be coated is a thermoplastic resin, and a polyethylene resin is often used particularly from the viewpoint of corrosion resistance. When polyethylene resin is used, even if solid matter adheres to the resin surface or the surface is roughened, the deformability of the polyethylene resin itself is high, so when the wire is tensioned from the PC steel in the grout, grout and PC The resin at the interface between the strands of the steel is easily deformed and the adhesion properties may be inferior.

  Accordingly, the main object of the present invention is to provide a coated PC steel stranded wire that has good adhesion to concrete and grout and has low friction against plastic and metal sheaths.

  The present invention achieves the above object by defining suitable adhesion to concrete and grout and suitable friction conditions for plastic and metal sheaths.

  That is, the coated PC steel strand of the present invention comprises a PC steel strand, a thermosetting resin coating layer formed on the surface thereof, and a granular material embedded so as to partially protrude from the coating layer. A coated PC steel strand inserted into a plastic sheath or metal sheath. The friction coefficient λ between the coated PC steel strand and the plastic sheath or metal sheath is λ ≦ 0.004, and the adhesion strength between the coated PC steel strand and the grout is the same as the adhesion strength between the bare PC steel strand and the grout. 90% or more. And all the said granular materials are comprised from particle | grains less than 75 micrometers.

  By limiting the friction coefficient and the bond strength, it is easy to insert the wire from the coated PC steel into the sheath, and it is possible to obtain a high adhesion with the grout, and a highly reliable PC structure. Objects and anchors can be configured.

  The friction coefficient λ is set to λ ≦ 0.004 from the design value of the friction coefficient λ when designing the prestress force of a normal structure (0.004) or the design value when designing a normal anchor force (0.004) This is because the load on the tension side is transmitted to the fixed side (fixing length side) without decreasing as much as possible. A specific method for obtaining the friction coefficient will be described in detail in a later embodiment.

  The prestressed concrete girder of the bridge is designed on the assumption that the fracture strength of the member is better than that of bare PC steel. Therefore, the adhesion characteristics between the sheath placed in the concrete of the girder and the grout injected between the coated PC steel strands are preferably at least 100% of the adhesion properties of bare PC steel, at best A limitation was made to ensure adhesion characteristics of 90% or more.

In addition, in order to prevent the wire from the coated PC steel from coming out from the anchor fixing length, the adhesion force between the grout and the PC steel wire is usually 0.78 MPa (8 kgf / Designed based on cm ² ). Therefore, the coated PC steel wire used for anticorrosion is also limited to ensure that the adhesion property of the wire PC is more than 100% of the adhesion property of bare PC steel. A specific method for evaluating the adhesion characteristics will be described in detail in a later example.

  The above friction characteristics and adhesion characteristics can be realized by defining the particle size distribution of the granular material embedded so as to partially protrude from the coating layer of the thermosetting resin. Hereafter, each structure of this invention coated PC steel strand is demonstrated.

  In the present invention, the particle size distribution of the granular material is composed of particles of less than 75 μm. The size of the granular material is based on the mesh opening size defined in JISZ8801-1994 “Test sieve”.

  By constituting all the granular materials with particles of less than 75 μm, the friction between the coated PC steel wire and the metal sheath or plastic sheath can be ≦ 0.004 in terms of the friction coefficient λ (friction coefficient in the case of linear arrangement). The friction between the sheath placed in the concrete of the prestressed concrete girder of the bridge and the inserted PC steel strand, the design value of the friction coefficient λ when designing the prestressing force of a normal structure (0.004 ) By making it smaller, it is possible to transmit the tension side load to the fixed side without reducing it as much as possible. In addition, due to this particle size distribution, in the case of anchors designed for normal anchoring force, the friction between the coated PC steel strand and the plastic sheath used to secure the free length is also used in anchors used on slopes, etc. The friction coefficient λ can be made smaller than the design value (0.004), and the load on the tension side can be transmitted to the anchor fixing length portion without being reduced as much as possible.

  In order to further reduce the friction coefficient λ, it is preferable to make the particle size finer. For example, it includes particles of more than 53 μm and less than 75 μm, and the content thereof is 80% by mass or less. Also, a friction coefficient λ of about 0.0015 to 0.0025 between a metal sheath (for example, a standard sheath “1000 sheath” manufactured by Steel String Equipment Co., Ltd.) and a bare PC steel wire used in a normal prestressed concrete girder is obtained. For this purpose, the grain size should be further reduced. That is, the particle size of 53 μm or less may be 60% by mass or more. The content of particles of 53 μm or less is preferably large, more preferably 80% by mass or more, and still more preferably all particles of 53 μm or less. When particles having a size exceeding 53 μm are contained, the size of the particles should be less than 75 μm.

The granular material is preferably inorganic hard particles. For example, one or more selected from the group consisting of SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , MgO and CaO can be mentioned.

  In order to partially embed the granular material in the coating layer and make the remaining portion protrude, the granular material is sprayed before the resin of the coating layer formed on the wire from the PC steel is cured, and then the resin is cured.

  On the other hand, a thermosetting resin is used for the material of the coating layer. In particular, it is preferable to use a resin that is deformed following the tension of the wire of PC steel and that is relatively hard. Specific examples include epoxy resins.

  As the method for forming the coating, powder coating or extrusion is suitable. In that case, it is desirable from the viewpoint of increasing the adhesion force that the strands of the PC steel wire are formed so as to appear on the surface of the coating layer. This coating layer only needs to be formed on the outer periphery of the strand of PC steel, but it is preferable in terms of anticorrosion that the resin is filled into the gaps between the strands. Filling the gaps between the strands with resin can be realized by once untwisting the wire from the PC steel, applying powder coating and then returning the twist, or pressurizing the molten resin in extrusion coating.

  The thickness of the coating layer is preferably 0.2 mm or more in order to prevent the granular material from penetrating the resin and reaching the wire of the PC steel, and to ensure reliable corrosion prevention by eliminating the pinhole.

  As explained above, according to the present invention coated PC steel wire, it is possible to reduce the friction with the sheath and increase the adhesion to the grout by limiting the particle size distribution of the granular material adhered to the coating. Can do.

  For concrete and girders of PC structures, it is possible to obtain a highly reliable structure with excellent adhesion characteristics to the metal sheath, plastic sheath, or grout injected into the protective tube of diagonal material. it can. In addition, the friction when inserting the cable into the sheath and the protective tube is small, and the coated PC steel can be easily inserted. Since the friction with the sheath is small even when the cable is tensioned, the load on the tension side can be transmitted to the fixed side without loss.

  The same is true for anchors. It has excellent adhesion characteristics with the grout of the fixing length portion injected into the drilling hole, and has little friction with the metal sheath and plastic sheath for the free length portion.

  Therefore, it can be used for prestressed concrete structures, inner cables for bridges, outer cables, diagonal cables for cable-stayed bridges, and cables for anchors such as slope reinforcement.

Embodiments of the present invention will be described below.
FIG. 1 is an explanatory view showing a manufacturing process of the coated PC steel strand of the present invention. Prepare a bare PC steel wire with a diameter of φ15.2mm in which 7 strands with a strand diameter of 5mm and a centerline of 5.2mm are twisted together. The bare PC steel strand 10 is supplied from the supply 1 to the pretreatment device 2, and the surface is cleaned by applying pretreatment with phosphoric acid while applying ultrasonic waves. After that, the bare PC steel strand 10 is introduced into the heating device 3 and heated to 250 ° C., then untwisted, and then passed through the coating device 4 to perform electrostatic powder coating with an epoxy resin. Subsequently, closed twisting is performed, and then introduced into the granular material adhering apparatus 5 to inject the powdery material onto the resin before curing, and adhere to a state in which a part of the powdery material is embedded and partly protrudes. . In order to accelerate the hardening, the resin-coated PC steel strand is introduced into the reheating device 6 and the resin coating is cured to such an extent that the strands of the wire appear from the PC steel. The wire 11 is then wound around the reel 8 after the cooling device 7 is introduced from the coated PC steel.

  As shown in FIG. 2, the resin is filled between the strands of the PC steel wire 20 by the above process, and the granular material 22 having a predetermined particle size distribution is partially formed before the epoxy resin 21 is cured. Embed and obtain a strand of coated PC steel with the remainder protruding from the surface of the coating layer.

As the granular material, a material mainly composed of MgO and SiO ₂ was used. All the particles of 75 μm or more have a size of 200 μm or less. The friction test between the wire and the sheath and the adhesion property test with the grout were performed on the coated PC steel with different particle sizes. For the friction test with the sheath, as shown in FIG. 3, a corrugated polyethylene sheath 30 having a rugged surface and inner surface (polyethylene sheath for main girder, φ35 mm outer diameter 41 mm, inner diameter 35 mm, manufactured by Totaku Industry Co., Ltd.) Using.

  In the test method, as shown in FIG. 4, a polyethylene sheath 30 is embedded almost linearly in a concrete plate 40 of about 20 m, and after the concrete is hardened, a coated PC steel wire 41 is inserted into the sheath. A pair of bearing plates are provided at both ends of the coated PC steel strand 41, and load cells 43 are arranged between the bearing plates 42, respectively. A jack 44 is attached to one end (tension end), and the other end (fixed end) is fixed by a fixing tool 45. Then, after tensioning from one end with the jack 44, the load cell 43 measured how much load was transmitted to the other end, and based on this, the friction coefficient between the wire and the sheath was obtained from the coated PC steel.

  In this test, in order to ensure that the wire of the coated PC steel was in sufficient contact with the sheath when tensioned, the arrangement was given a slight curvature (R = 2000 m). FIG. 5 shows a cross section of the coated PC steel wire in the sheath. The coated PC steel strand 41 is arranged in the sheath 30 so as to be biased toward the inside of the curvature, and is in contact with the inner surface of the sheath.

P = Po × e ^{− (μα + λl)} P = Load at the fixed end (kgf or N)
Po = Load at tension end (kgf or N)
l = Length from tension end to fixed end (m)
α = full angle change from tension end to fixed end (rad.)
λ = friction coefficient per length (1 / m)
μ = coefficient of friction per angle (1 / rad.)

  Here, the friction coefficient μ is a value when the wire is bent and arranged from the coated PC steel. In this test, μα = 0 is set because of a substantially linear arrangement.

  Using the same test method, several coated PC steel strands with different particle size distributions were used for a polyethylene sheath with a smooth sheath inner surface and a metal sheath with a concave portion on the sheath inner surface. The test was conducted. As the polyethylene sheath, JISK6761 “General-purpose polyethylene pipe” with a nominal diameter of 30 mm was used. As the metal sheath, a standard type 1000 and a sheath name 1035 manufactured by Steel String Equipment Co., Ltd. were used. As shown in FIG. 6, this metal sheath is formed in a pipe shape by wrapping a steel plate having a predetermined width having an annular protrusion having a width of 6 mm at a constant width. The hatched portion in FIG. 6 is where the steel plates are lapping. The annular protrusion has an inclination with respect to the circumferential direction. The maximum outer diameter of the annular protrusion is 38 mm, and the outer diameter of the portion excluding the protrusion is 35 mm. The material was JISG3141 (cold rolled steel sheet).

Next, the adhesion test with grout was carried out by a method according to “Concrete Pull-out Test Method” of Japan Concrete Institute. As shown in FIG. 7, a coated PC is placed in a concrete block 61 having a 20 cm cubic shape, an inside diameter of 16 cm, a round reinforcing bar 60 having a diameter of 6 mm, and a mortar strength of 25.7 MPa (262 kgf / cm ² ). The steel strand 62 is fixed. The wire 62 was drawn from this coated PC steel, the load at that time was measured, and thereby the bond strength of the wire was obtained from the coated PC steel. The bond strength was evaluated by the maximum load at the time of drawing and the initial sliding load at which the end of the wire slips 0.025mm from the coated PC steel.

  These tests were also conducted on bare PC steel strands and other coated PC steel strands as comparative materials. The bare PC steel strand has the same composition, the same size and the same number of strands as the above-mentioned coated PC steel strand except that there is no resin coating. The configuration of each comparative material is shown below.

  <Comparative material 1>... FIG. 8 Bare PC steel wire 70 with a diameter of 15.2 mm.

<Comparison material 2> ............ Figure 9 (Japanese Patent Publication No. 3-28551)
It is a coated PC steel wire that does not use powder. A coating layer 81 of epoxy resin is provided on the surface of a bare PC steel strand of φ15.2 mm. The covering layer is formed so that the strands of the wire 80 appear from the bare PC steel, and the granular material is not embedded. Resins are also filled in the gaps between the strands.

<Comparison material 3> ... Figure 10 (Japanese Patent Publication No. 3-28551)
The coated PC steel wire using the powder and granular material. A coating layer 91 made of epoxy resin is provided on the surface of a stranded wire 90 of φ15.2 mm bare PC steel. The covering layer 91 is formed such that the strands of the wire appear from the bare PC steel, and the granular material 62 is embedded so as to partially protrude. The particle size distribution of the granulate is about 70-200 μm. Resins are also filled in the gaps between the strands.

<Comparative material 4> ....... FIG. 11 (Japanese Patent Laid-Open No. 8-42062)
It is a twisted coated PC steel strand. After heating the wire 100 from bare PC steel of φ15.2mm to 360 ℃, extrude polyethylene with good adhesion while applying pressure so that the coating film thickness is about 0.1mm and more Pass the dice so that appears. Thereafter, high density polyethylene is further coated by extrusion to make the film thickness about 0.4 mm. At the time of the last extrusion process, a creased coating layer 101 is formed through a die so that crease-like irregularities having an angle with respect to the axial direction of the strand of the PC steel are formed on the coating surface.

  Table 1 shows the particle size distribution, the friction coefficient, and the adhesion property test results of the powder.

  From these results, the adhesion characteristics for the ones with embedded granular materials satisfy both the initial sliding load and the maximum load of 90% or more of bare PC steel.

Regarding the friction coefficient, the following became clear.
(1) Satisfying λ ≦ 0.004 by making the particles less than 75 μm.
(2) When the particle size of 53 μm or less is 60 mass% or more, λ ≦ 0.0025 that is almost equivalent to that of bare PC steel is satisfied.
(3) Sufficient adhesion strength can be obtained even if most of the granular materials have a size of 20 μm or less.

  The coated PC steel strand of the present invention can be used for prestressed concrete structures, inner cables in bridges, outer cables, diagonal cables in cable-stayed bridges, and cables in anchors for slope reinforcement.

It is explanatory drawing which shows the manufacturing process of this invention covering PC steel strand. It is a cross-sectional view of the stranded wire of the present invention coated PC steel. It is a partial longitudinal cross-sectional view of a polyethylene sheath. It is explanatory drawing of a friction test method. It is a cross section which shows the arrangement | positioning state of the strand from the coated PC steel in the sheath. It is explanatory drawing of a metal sheath. It is explanatory drawing of an adhesion test method. 3 is a cross-sectional view of a comparative material 1. FIG. 3 is a cross-sectional view of a comparative material 2. FIG. 3 is a cross-sectional view of a comparative material 3. FIG. 6 is a cross-sectional view of a comparative material 4. FIG. It is the schematic of an anchor structure. It is the schematic which shows the girder part of a bridge.

Explanation of symbols

1 Supply
2 Pretreatment device
3 Heating device
4 Coating equipment
5 Granule adhesion device
6 Reheating device
7 Cooling device
8 reel
10 Bare PC steel stranded wire
11 Coated PC steel strand
20 PC steel stranded wire
21 Epoxy resin
22 Granules
30 Polyethylene sheath
40 Concrete board
41 Coated PC steel strand
42 Bearing plate
43 Load cell
44 Jack
45 Fixing tool
60 Reinforcing bars
61 Concrete block
62 Coated PC steel strand
70 Bare PC steel strand
80 Bare PC steel strand
81 Coating layer
90 Bare PC steel strand
91 Coating layer
100 Bare PC steel strand
101 Cover layer with folds
110 drilling
111 PC steel strand
112 Grout
113 pedestal
114 Bearing plate
115 Fixing tool
120 digits
121 sheath
122 PC steel strand
123 Grout

Claims (4)

PC steel stranded wire, thermosetting resin coating layer formed on its surface, and granular material embedded so as to partially protrude from the coating layer, inserted into a plastic sheath or metal sheath Coated PC steel strand,
All of the granules are composed of particles less than 75 μm,
The friction coefficient λ between this coated PC steel strand and the plastic sheath or metal sheath is λ ≦ 0.004,
A coated PC steel stranded wire characterized in that the adhesion strength between the coated PC steel strand and the grout is 90% or more of the adhesion strength between the bare PC steel and the grout.   2. The coated PC steel strand according to claim 1, wherein the granular material includes particles of more than 53 μm and less than 75 μm, and the content thereof is 80% by mass or less.   2. The coated PC steel strand according to claim 1, wherein the granular material contains particles of 53 μm or less in an amount of 60% by mass or more.   2. The coated PC steel strand according to claim 1, wherein all of the granular materials are composed of particles of 53 μm or less.

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