JP7659461B2 - Corrosion prevention method for structural cables and structural cables treated with the corrosion prevention method - Google Patents

Description

The present invention relates to a corrosion prevention technique for existing structural cables that are used in suspended structures such as suspension bridges and cable-stayed bridges and are exposed outdoors, or for new structural cables that are exposed outdoors, and in particular to a corrosion prevention method that aims to extend the life of structural cables when preventing corrosion of such structural cables or when the structural cable becomes corroded (rather than replacing the structural cable when corrosion is minor and replacement is difficult), and to a structural cable that has been treated with this corrosion prevention method.

Structural cables used in suspension bridges and cable-stayed bridges are exposed to harsh outdoor weather conditions and therefore require painting to prevent deterioration such as rust. Traditionally, structural cables were painted with weather-resistant paint, but the harsh weather conditions to which the painted structural cables were exposed could require periodic repainting. However, due to the poor accessibility of such structural cables caused by the fact that they are installed on the main towers at high positions in suspension bridges and cable-stayed bridges, this repainting required a considerable amount of money. Furthermore, in order to repaint properly, the existing paint must be removed before repainting, which further increases costs.

In contrast to such repairs by repainting, it has recently been discovered that structural cables can be protected from outdoor exposure more permanently by spirally wrapping a polychloroprene covering material such as neoprene (the covering material can be in the form of a tape that can be easily wrapped in a spiral shape, for example) around structural cables of different lengths at different locations, even in a single suspended structure. However, this type of neoprene covering material needs to match or harmonize with the appearance of other elements (girders, towers, hangers, etc.) other than the structural cables in the suspended structure (suspension bridge, cable-stayed bridge, etc.) in which it is used, but it is usually not possible to properly color it before construction. Therefore, after spirally wrapping the bridge structural cables in neoprene covering material, the exterior of the covering material is painted to properly match the color between the structural cables and other bridge elements, but this type of painting process is very time-consuming and therefore very expensive.

Furthermore, when structural cables for suspension bridges are wrapped helically with neoprene tape, it is important that each turn of tape be firmly bonded to the preceding turn to adequately seal the seam between them and thereby prevent the ingress of moisture and dust at the interface between the cover and the structural cables. It has been found that when using this type of neoprene tape (wrapped helically around the structural cables), a reliable and adequate seal can be achieved by providing a significant overlap between successive turns of tape and using a solvent to bond the overlapping layers together. However, the application of the solvent is laborious and therefore expensive, and many of the solvents present environmental, health and safety problems and require careful handling and disposal.

In view of these various problems, U.S. Patent No. 5,390,386 (Patent Document 1) discloses a corrosion prevention method for outdoor-exposed structural cables used in suspension bridges and cable-stayed bridges, which can be advantageously protected from exposure to severe weather conditions by spirally wrapping the structural cables with a flexible and suitable synthetic rubber chlorosulfonated polyethylene material. The corrosion prevention method disclosed in Patent Document 1 is a method for protecting structural cables used in suspension bridges, cable-stayed bridges, etc. by spirally wrapping a flexible synthetic rubber tape (chlorosulfonated polyethylene) around the structural cables. The wrapping method involves wrapping the tape in a half-wrap, overlapping each half to form a double layer of uniform thickness, and then heating the tape to heat-seal the overlapped layers to seal the seams, and shrinking the tape to reliably and sufficiently fit (integrate) the synthetic rubber tape (chlorosulfonated polyethylene) to the structural cables. According to this corrosion prevention method, by wrapping a synthetic rubber tape (chlorosulfonated polyethylene) around the corroded structural cables, it is possible to prevent the infiltration of air and moisture, and to slow the progression of corrosion. Furthermore, since such flexible synthetic rubber tape can be colored before carrying out the corrosion prevention method, it is possible to properly color match the structural cables with other elements by coloring the flexible synthetic rubber tape the same color as the structural cables were originally colored.

U.S. Pat. No. 5,390,386

However, in the corrosion prevention method disclosed in Patent Document 1, the structural cable wrapped with the tape (or sheet) used for corrosion prevention as a coating material makes the cable itself invisible due to the coating material, so after construction, it is not possible to visually check the deterioration status of the structural cable's components (the presence or absence and progress of rust in the structural cable (steel material) itself, the presence or absence and progress of rust in the rust prevention layer in the structural cable (steel material) such as zinc plating, wax, or rust prevention paint, the deterioration status of the outer tube such as a PE pipe (polyethylene pipe), etc.). Therefore, at present, in order to check the deterioration status of the structural cable's components, it is necessary to remove the coating material formed by the tape (or sheet) used for corrosion prevention, or to check using a non-destructive inspection method that can detect rust, etc., which poses the problem of extremely poor workability.

The present invention was developed in consideration of the above-mentioned problems with the prior art, and its purpose is to provide a corrosion prevention method for existing structural cables that are used in suspended structures such as suspension bridges and cable-stayed bridges and are exposed outdoors, or for new structural cables that are exposed outdoors, which can prevent corrosion of such structural cables, or in the event that the structural cable becomes corroded (instead of replacing the structural cable when the corrosion is minor and replacement is difficult), and which makes it easy to visually check the deterioration and other conditions of the structural cable's components after the application of a corrosion prevention method that aims to extend the life of the structural cable, and to provide a structural cable that has been treated with this corrosion prevention method.

In order to achieve the above-mentioned object, the corrosion prevention method for a structural cable and the structural cable to which the corrosion prevention method has been applied according to the present invention have the following technical means.
In other words, a corrosion protection method for structural cables relating to one aspect of the present invention is a corrosion protection method for structural cables exposed to the outdoors and used in suspended structures including suspension bridges and cable-stayed bridges, and is characterized in that the structural cable is wrapped and covered in a visible, transparent, and weldable thin resin film.

Preferably, the resin is a fluororesin.
More preferably, the resin thin film is tape-shaped, and the tape-shaped resin thin film is overlapped over at least a portion of the tape width and spirally wound around the structural cable, thereby enveloping and covering the structural cable with the tape-shaped resin thin film.

More preferably, the resin thin film is in sheet form, and the sheet-like resin thin film is wrapped around the structural cable so that the sheet-like resin thin film forms a single-layer tube, and the ends of the sheet in a direction perpendicular to the longitudinal direction of the structural cable are overlapped, thereby wrapping and covering the structural cable with the sheet-like resin thin film.
More preferably, the resin thin films may be laminated together, and then the laminated portions may be heated and thermally welded.

More preferably, a substance that reacts to water or moisture may be disposed between the structural cable and the thin resin film.
In addition, a structural cable treated with a corrosion prevention method according to another aspect of the present invention is characterized in that it is an outdoor-exposed structural cable used in suspended structures, including suspension bridges and cable-stayed bridges, which has been treated with any of the corrosion prevention methods described above.
Preferably, the structural cable may be configured so that a structure is provided in which dry air supplied from outside the structural cable flows between the thin resin film and the structural cable.

The corrosion prevention method and structural cable treated with the corrosion prevention method according to the present invention are used in suspended structures such as suspension bridges and cable-stayed bridges, and are used for existing structural cables exposed outdoors, or for newly installed structural cables exposed outdoors. When corrosion of such structural cables is prevented, or when the structural cable becomes corroded (instead of replacing the structural cable when corrosion is minor and replacement is difficult), the deterioration of the structural cable's components can be easily visually confirmed after the application of the corrosion prevention method, which aims to extend the life of the structural cable, and a structural cable treated with the corrosion prevention method can be provided.

This is a diagram to explain a corrosion protection method for structural cables in an embodiment of the present invention, in which a structural cable is wrapped and covered with a transparent fluororesin (preferably ETFE) tape, where (A) it is spirally wrapped with less than a half wrap, and (B) it is spirally wrapped with a half wrap. 1 is a diagram for explaining the state in which a structural cable is wrapped and covered with a transparent fluororesin (preferably ETFE) sheet in a corrosion protection method for a structural cable according to an embodiment of the present invention. FIG. 3 is a diagram showing the state in which an air blowing and drying system is applied to a structural cable that has been subjected to a corrosion protection method in which the structural cable is wrapped and covered with a fluororesin (preferably ETFE) sheet as shown in FIG. 2 . FIG. 2 is a diagram showing the state in which an air blowing and drying system is applied to a structural cable that has been subjected to a corrosion protection method in which the structural cable is wrapped and covered with a fluororesin (preferably ETFE) tape as shown in FIG. 1(A).

The following describes in detail the corrosion prevention method for structural cables according to an embodiment of the present invention and the structural cable to which the corrosion prevention method has been applied with reference to the drawings. The structural cable to which the corrosion prevention method for structural cables according to the embodiment of the present invention has been applied as described below is the structural cable (to which the corrosion prevention method has been applied) according to the embodiment of the present invention. In the following description, the corrosion prevention method for existing structural cables used in suspended structures such as suspension bridges and cable-stayed bridges and exposed outdoors is described as a corrosion prevention method for extending the life of the structural cable when the structural cable is corroded (instead of replacing the structural cable when the corrosion is minor and replacement is difficult), but the corrosion prevention method according to the present invention is not limited to being applied to existing structural cables exposed outdoors, and may also be applied as a corrosion prevention method for preventing corrosion of newly installed structural cables exposed outdoors.

The figures referred to in the following explanation are basically schematic diagrams that omit detailed structures in order to facilitate understanding of the present invention, and may show parts that should be shown in their external form rather than their internal form as if they were seen through to the inside, parts that should be shown in cross sections rather than in their external form may be shown in their external form, and parts that should be shown in their external form rather than in their cross sections may be shown in cross sections.

A corrosion protection method for structural cables according to an embodiment of the present invention will be described in detail with reference to Figures 1 to 5. Figure 1 shows a corrosion protection method for structural cables according to the present embodiment, in which a fluororesin (preferably ETFE) tape is used as a weldable resin thin film, and Figure 2 shows a corrosion protection method for structural cables according to the present embodiment, in which a fluororesin (preferably ETFE) sheet is used as a weldable resin thin film.
As shown in these FIGS. 1 and 2, the corrosion protection method for structural cables according to the present embodiment includes the following steps:
It has the following features:

The corrosion prevention method for structural cables according to the present embodiment is a corrosion prevention method for structural cables exposed outdoors and used in suspended structures including suspension bridges and cable-stayed bridges, in which the structural cables are wrapped and covered with a transparent and weldable resin thin film that allows the structural cables to be seen. As described below, the material for the transparent and weldable resin thin film that allows the structural cables to be seen is preferably a transparent fluororesin, and particularly preferably ETFE. As described below, the shape of the transparent and weldable resin thin film that allows the structural cables to be seen is preferably a tape or sheet shape, and is transparent so that the structural cables can be seen even after construction. Here, visibility originally means recognizing (the condition of the structural cables, such as deterioration, after construction of the corrosion prevention method according to the present invention) by sight, which is one of the five human senses, but in the present invention, it also includes recognizing) the condition of the structural cables, such as deterioration, after construction of the corrosion prevention method according to the present invention, by taking an image using a device other than a human, such as a camera, and analyzing the image data.

Here, the material of this thin resin film is preferably a fluororesin, and among fluororesins, transparent ETFE (ethylene tetrafluoroethylene, ethylene-tetrafluoroethylene copolymer) is particularly preferred.
Fluorocarbon polymers is a general term for synthetic resins obtained by polymerizing olefins containing fluorine. They are characterized by their high heat resistance and chemical resistance and their small coefficient of friction. The fluororesin that is produced most in large quantities is polytetrafluoroethylene (tetrafluororesin). It has high resistance to chemicals and electrical insulation, the lowest coefficient of friction of its surface among known substances, and is stable at high temperatures and non-flammable, so it is used as an engineering plastic. This polytetrafluoroethylene, which was first developed, has a heat resistance of 260°C, but does not exhibit thermoplasticity and is not suitable for processability. In order to improve moldability, various chlorotrifluoroethylene resins and polyvinylidene fluoride resins have been developed in which part of the fluorine group of the completely fluorinated polytetrafluoroethylene is replaced with hydrogen or chlorine, or is made into an olefin. Although these resins are inferior to polytetrafluoroethylene in terms of heat resistance, they are highly processable and can be compressed, extruded, and injected.

(1) Fully fluorinated resins include polytetrafluoroethylene (tetrafluororesin, abbreviated as PTFE), (2) partially fluorinated resins include polychlorotrifluoroethylene (trifluororesin, abbreviated as PCTFE or CTFE), polyvinylidene fluoride (abbreviated as PVDF), and polyvinyl fluoride (abbreviated as PVF), and (3) fluorinated resin copolymers include perfluoroalkoxy fluorine resin (abbreviated as PFA), tetrafluoroethylene-hexafluoropropylene copolymer (abbreviated as FEP), ethylene-tetrafluoroethylene copolymer (abbreviated as ETFE), and ethylene-chlorotrifluoroethylene copolymer (abbreviated as ECTFE).

On the other hand, polyethylene (PE), a representative of common synthetic resins, is a resin with the simplest molecular structure and is mass-produced at low cost, but its strength and heat resistance are extremely weak. This characteristic means that it is a resin with good thermal responsiveness, and since it can be easily molded at relatively low temperatures, it can also be said to be a very easy-to-use resin. For this reason, PVDF and ETFE were developed as resins that have the properties of both PE and PTFE, and both are combinations (copolymerizations) of PE parts (C2H4) and PTFE parts (C2F4). Unlike PVDF, which is roughly copolymerized, ETFE is carefully alternatingly polymerized. PE chains are the cause of deterioration, but PE chains are reduced in ETFE by carefully alternating polymerization through devising reaction conditions, etc. The mobility of the PE portion reduces the melt viscosity of ETFE, and it softens at just under 180°C, making it possible to perform extrusion molding such as film formation. At the same time, the decomposition between the PE portions due to radicals is blocked by F, making it extremely resistant to decomposition by ultraviolet rays and the like. Therefore, it is preferably used in applications where it is not used in high-temperature environments but weather resistance is required. In this way, ETFE combines the properties of PTFE and PE, has better moldability than PTFE, and can be injected or molded into a film, and can be easily processed into tape or sheet form. In addition, it can be colorless and transparent, colored and transparent, or opaque, and resin thin films of various colors (including transparent) can be realized.

It should be noted that ETFE welding does not require half-wrapping because strength can be obtained even with a narrow bonding width (overlap width). For this reason, when a transparent fluororesin tape (particularly ETFE tape) is used instead of an opaque synthetic rubber tape, the weight per unit length of the fluororesin tape itself is lighter than that of the synthetic rubber tape, and further, since the ETFE tape is overlapped by about 1/4 of the width to form an incomplete double structure rather than overlapped by about 1/2 of the width to form a complete double structure, the corrosion prevention method shown in Figure 1 (A) significantly improves workability (in addition to improving the visual confirmation workability by easily visually confirming the deterioration of the structural cable components after the corrosion prevention method is applied, since the structural cable is wrapped in a visible, transparent, and weldable ETFE tape that can be welded.) compared to the corrosion prevention method disclosed in Patent Document 1 (half-wrapped with synthetic rubber), the corrosion prevention method shown in Figure 1 (A) significantly improves workability (in addition to improving the visual confirmation workability by easily visually confirming the deterioration of the structural cable components after the corrosion prevention method is applied, since the structural cable is wrapped in a visible, transparent, and weldable ETFE tape that can be welded. Furthermore, because the weight per unit length of the fluororesin tape itself is lighter than that of the synthetic rubber tape, the corrosion prevention method shown in Figure 1 (B) (half-wrapped with thin resin film) has improved workability compared to the corrosion prevention method disclosed in Patent Document 1 (half-wrapped with synthetic rubber).

In addition, the resin thin film is preferably in the form of a tape (ETFE tape), and the tape-like resin thin film is wrapped around the structural cable in a spiral shape by overlapping less than half the tape width (however, the present invention does not exclude less than half wraps (about 1/4 wraps) in which less than half the tape width (for example, about 1/4) is overlapped and wrapped around the structural cable in a spiral shape). In this case, the half wrap disclosed in Patent Document 1 overlaps half the tape width and wraps it in a spiral shape, so that the complete synthetic rubber tape covering layer (wrapping layer) forms a complete two-layer structure, whereas in this embodiment, it includes an incomplete two-layer structure in which less than half the tape width (for example, about 1/4) is overlapped and has a single-layer portion. Then, after overlapping the resin thin films, it is preferable to heat and heat-seal the overlapped portion (here, the portion overlapped by about half or less than half the tape width, i.e., about 1/4). In this way, in the corrosion protection method for structural cables according to the present embodiment, a transparent fluororesin tape (ETFE tape) is used instead of an opaque synthetic rubber tape as in Patent Document 1, and a coating layer is formed on the structural cable in an incomplete two-layer structure (partially one-layer structure) that is an optional configuration (not a complete two-layer structure with half-wrap, but an overlap of less than half the tape width (approximately 1/4 of the tape width)), so that the weight of the coating material is reduced as described below (the structural cable is wrapped in a transparent and weldable ETFE tape that allows the structural cable to be seen, and the deterioration of the structural cable components can be easily visually confirmed after the corrosion protection method is applied, thereby improving the visual confirmation workability). Note that the present invention is not particularly limited to the width of the tape to be overlapped, as long as the tape-shaped resin thin film is overlapped at least partially over the tape width and wound spirally around the structural cable.

Here, with reference to FIG. 1, a mode in which a tape-shaped resin thin film (ETFE tape) is spirally wound around a structural cable to encase and cover the structural cable with the tape-shaped resin thin film will be described.
Fig. 1(A) shows a state where the ETFE tape 150 is wound spirally with less than half-lap (approximately 1/4 of the tape width) overlapping, and Fig. 1(B) shows a state where the ETFE tape 150 is wound spirally with half-lap. Note that the cable wire 110 may be directly coated with anticorrosive paint without providing an outer jacket tube 120 for anticorrosive purposes.

The state shown in Figure 1 (A) shows a structural cable 100 in the middle of undergoing corrosion protection work, in which the cable wire 110 and the outer jacket tube (an FRP tube, PE tube, etc. for corrosion protection purposes) 120 covering the outer periphery of the cable wire 110 are spirally wrapped with ETFE tape 150 with less than a half wrap, and the structural cable is wrapped in a tape-like resin thin film.

The state shown in FIG. 1(B) shows a structural cable 102 in the middle of undergoing anticorrosion construction work.
The cable wire 110 and the outer tube (PE tube) 120 covering the outer periphery of the cable wire 110 are spirally wrapped with an ETFE tape 152 in a half-wrap manner, so that the structural cable is enveloped in a tape-like resin thin film.
1(A) and 1(B), the overlapping portions (about 1/4 of the tape width) of the ETFE tapes 150 spirally wound around the cable wire 110 and the outer tube (PE tube) 120, or the overlapping portions (about 1/2 of the tape width) of the ETFE tapes 152 are heated and thermally welded. This thermal welding welds the ETFE tapes together, suppressing the intrusion of air and moisture from the overlapping portions and slowing the progress of corrosion.

Furthermore, since the structural cable is wrapped in a visible, transparent, and weldable thin resin film (here, ETFE tape 150 or ETFE tape 152), it is preferable in that the deterioration and other conditions of the components of the structural cable can be easily visually confirmed after the corrosion prevention method is applied.
Next, referring to Figure 2, we will explain an embodiment in which a sheet-shaped resin thin film (ETFE sheet) is wrapped around a structural cable so that the sheet-shaped resin thin film forms a single-layer tube, and the ends of the sheet in a direction perpendicular to the longitudinal direction of the structural cable are overlapped to wrap and cover the structural cable with the sheet-shaped resin thin film.

Figure 2 shows a structural cable 104 in the middle of undergoing anti-corrosion construction, in which a single ETFE sheet 160 is wrapped around the cable wire 110 and an outer tube (corrosion-resistant FRP pipe, PE pipe, etc.) 120 that covers the outer periphery of the cable wire 110 to form a single-layer tube, and the sheet ends 162 perpendicular to the longitudinal direction of the structural cable are overlapped, so that the structural cable is wrapped in a sheet-like thin resin film.

Even in the case of FIG. 2, one ETFE sheet 160 is wrapped around the cable wire 110 and the outer tube (PE tube) 120 to form a single-layer tube, and the overlapping portions of the sheet ends 162 of the ETFE sheet 160 are heated and thermally welded. This thermal welding welds the sheet ends 162 of the ETFE sheet 160 together, suppressing the infiltration of air and moisture from the overlapping portions and slowing the progression of corrosion.

It should be noted that since the ETFE sheet is strong enough even as a single layer (completely single-layered structure), there is no need to half-wrap it to create a complete double-layered structure. For this reason, when using a fluororesin sheet (particularly an ETFE sheet) instead of a synthetic rubber tape, the weight per unit area of the fluororesin sheet itself is lighter than that of the synthetic rubber tape, and further, since the ETFE sheet is made into a completely single-layered structure rather than half-wrapped to create a completely double-layered structure by overlapping the ETFE tape by about 1/2 the width, the weight of the covering material can be significantly reduced, and therefore the corrosion prevention method shown in Figure 2 has significantly improved workability compared to the corrosion prevention method disclosed in Patent Document 1 (half-wrapped with synthetic rubber).

In addition, there may be an air gap between the outer tube 120 covering the outer periphery of the cable wire 110 and the ETFE sheet 160, as long as the infiltration of air and moisture from the outside to the inside of the covering material can be suppressed.
Furthermore, since the structural cable is wrapped in a visible, transparent, and weldable thin resin film (here, ETFE sheet 160), this is advantageous in that the deterioration and other conditions of the structural cable's components can be easily visually confirmed after the corrosion prevention method is applied.

Here, whether in the embodiment shown in Fig. 1 or the embodiment shown in Fig. 2, it is also preferable to place a substance that reacts to moisture or humidity between the structural cable and the thin resin film (ETFE tape 150, ETFE tape 152, or ETFE sheet 160). As described above, the problem with the prior art is that the tape (or sheet) used for corrosion protection cannot visually check the deterioration status (presence or absence of rust and its progress in the structural cable (steel material) itself, presence or absence of rust and its progress in the rust prevention layer in the structural cable (steel material) such as zinc plating or wax, deterioration status of the outer tube such as a PE pipe (polyethylene pipe), etc.). In contrast, in the corrosion protection method for structural cables according to the present embodiment, as described above, a transparent fluororesin (preferably TEFE, which has excellent weather resistance) tape or fluororesin (preferably TEFE, which has excellent weather resistance) sheet is used, and since the covering material is transparent even after the application of the corrosion protection method for structural cables, the deterioration status of the structural cable (presence or absence of rust and its progress in the structural cable (steel material) itself, presence or absence of rust and its progress in the rust prevention layer in the structural cable (steel material) such as zinc plating or wax, deterioration status of the jacket tube such as a PE pipe (polyethylene pipe), etc.) can be visually confirmed. Note that the "transparent" of the resin thin film in the corrosion protection method according to the present invention includes both "colorless transparent" and "colored transparent", and is not particularly limited to "colorless transparent" or "colored transparent" as long as it allows visual confirmation of the deterioration status of the structural cable after the application of the corrosion protection method according to the present invention. In this respect, it is not possible to visually check the deterioration of the structural cable after the application of the corrosion prevention method of the present invention; for example, "opaque (only)" is excluded from the "transparent" of the thin resin film in the description of the present invention.

In addition, it is preferable to place a powder, paint, or sheet that discolors or changes in quality due to moisture or humidity between the structural cable and the thin resin film (TEFE tape, TEFE sheet). This makes it possible to visually check the intrusion of moisture, which is a cause of corrosion, and helps to determine the progress of corrosion of the steel material. In this way, the use of microcapsules, silica gel, and cobalt chloride hexahydrate as materials that discolor or change in quality due to moisture or humidity, and water-absorbing sheets as materials that change in quality due to moisture or humidity are considered.
The corrosion protection method for structural cables according to the present embodiment described above will now be described in more detail.

As described above, there are two possible cases for structural cables used in suspended structures such as suspension bridges and cable-stayed bridges: (1) cables protected from corrosion by being covered with an outer tube such as an FRP (reinforced plastic) pipe or a PE (polyethylene) pipe; and (2) cables protected from corrosion by having an anticorrosive paint applied directly to the cable. The implementation form differs depending on the case.
Furthermore, with regard to the scope of application of the corrosion protection method for structural cables in this embodiment, it may be applied over the entire length of the structural cable that is the target of the corrosion protection method, or it may be applied only to the parts that have been deformed and to which it is desired to impart waterproofing and airtightness.

[1] Cable protected from corrosion by covering with an outer tube such as an FRP or PE pipe When only a part of the outer tube is damaged but the majority of the outer tube is sound, ETFE tape is wrapped directly around the outer tube. There are two wrapping methods, the embodiment shown in Fig. 1 and the embodiment shown in Fig. 2. If the outer tube is severely damaged and cannot be directly wrapped with tape, the outer tube is removed and the same treatment as for the cable protected from corrosion by directly applying an anticorrosive paint is carried out as described below in [2].

[2] Cables protected against corrosion by directly applying an anticorrosive paint If the unevenness of the cable surface is small and the tape can fit, the same treatment as [1] is applied. However, if the surface is very uneven, for example because multiple cables are bundled together, the uneven parts are filled with molding material to smooth out the unevenness, and then the same treatment as [1] is applied.
In this case, it is preferable to use transparent resin or transparent clay as the covering material (molding material) so that the inside of the steel material (cable) can be seen, and it is also desirable to place a substance that will discolor or change quality when exposed to moisture or humidity, as described below, to make the intrusion of corrosion factors visible.

These are explanations about how, after the application of corrosion protection methods for structural cables, it is possible to visually check the deterioration status of the structural cables (the presence or absence and progress of rust in the structural cable (steel) itself, the presence or absence and progress of rust in the anti-rust layer of the structural cable (steel) such as zinc plating or wax, the deterioration status of the outer pipe such as a PE pipe (polyethylene pipe), etc.).
Next, visual confirmation of corrosion of structural cables (steel materials) will be described. Since the corrosion rate of structural cables (steel materials) varies greatly depending on the external environment, when the corrosion rate is slow, the judgment of the progress of corrosion may differ depending on the worker who performs the visual confirmation or the frequency of the visual confirmation. Therefore, if the following measures are taken to visualize the penetration of corrosion factors, the internal visual confirmation effect of this embodiment will have a more beneficial effect.

- Method for visualizing the infiltration of corrosion factors The presence or absence of moisture is a major factor in the corrosion of structural cables used in suspension bridges, cable-stayed bridges, and other structures, which are the subject of the corrosion protection method for structural cables according to the present invention. Therefore, visualization of the infiltration of moisture or moisture is important as a criterion for judging the progress of corrosion. Therefore, in this embodiment, a method for visualizing the infiltration of moisture or moisture even through a transparent thin fluororesin film is to place a substance that discolors or changes in quality due to moisture or moisture. Specific examples include the following substances.

(1) Water-soluble microcapsules containing a dye. When moisture penetrates, the microcapsules break down and the dye is released, thereby detecting the presence of water.
(2) Silica gel used for dehumidification, etc. This is detected by the discoloration of silica gel due to moisture or humidity. This method is expected to have an anti-corrosion effect on structural cables (steel materials) during the period when the silica gel absorbs moisture or humidity.
(3) Cobalt chloride hexahydrate powder or solution. It is detected by the change in color due to moisture or humidity.
(4) Water-absorbent sheet: When water is absorbed, its volume expands, and this change in volume can be detected visually.

In addition, with these visualization methods, it is preferable to arrange the structural cables (steel materials) in a way that allows them to be seen, as covering the entire structure makes it impossible to see the condition of the structural cables (steel materials). However, it is acceptable to cover the entire structure, as the presence of moisture affects the progression of corrosion.
In this way, the structural cable is covered with a thin, transparent resin film that allows visual confirmation of the deterioration of the structural cable's components (deformations such as the presence or absence and progression of rust in the structural cable (steel) itself, the presence or absence and progression of rust in the rust-preventive layer of the structural cable (steel) such as zinc plating or wax, and the deterioration of the jacket pipe such as a PE pipe (polyethylene pipe)). Furthermore, by visualizing the intrusion of moisture or humidity, which is the cause of the deterioration, the accuracy of visual detection of abnormalities can be improved.

As described above, the structural cable treated with the corrosion prevention method according to the present embodiment and the structural cable treated with the corrosion prevention method are corrosion prevention methods for outdoor exposed structural cables used in suspended structures such as suspension bridges and cable-stayed bridges, and when such a structural cable becomes corroded (especially when the corrosion is minor and replacement is difficult), the structural cable is not replaced but rather the deterioration of the structural cable components can be easily visually confirmed after the application of the corrosion prevention method, which aims to extend the life of the structural cable, and a structural cable treated with the corrosion prevention method can be provided.

<Modification>
A modified example of the embodiment of the present invention will be described below. This modified example is a case where an air blowing and drying system is applied to a structural cable to which the anticorrosion method of the present invention has been applied (i.e., a case where a structural cable to which the anticorrosion method of the present invention has been applied is suitably provided with an air blowing and drying function), and will be described with reference to Fig. 3 and Fig. 4. Here, Fig. 3 is a diagram showing a state where an air blowing and drying system is applied to a structural cable to which the anticorrosion method of wrapping and covering the structural cable with a fluororesin (preferably ETFE) sheet shown in Fig. 2 has been applied, and Fig. 4 is a diagram showing a state where an air blowing and drying system is applied to a structural cable to which the anticorrosion method of wrapping and covering the structural cable with a fluororesin (preferably ETFE) tape shown in Fig. 1(A) has been applied.

As with the anticorrosion method of the present invention, this air supply drying system can be suitably applied to structural cables that have been subjected to the anticorrosion method of the present invention, whether they are existing structural cables or newly constructed structural cables. In addition, in the above-mentioned embodiment, the outer jacket tube 120 such as a PE pipe is included in the description, but in the present invention, this outer jacket tube 120 is not a required component, and the following modified examples will be described as not including this outer jacket tube 120. The above-mentioned embodiment does not require the outer jacket tube 120, and in the modified examples shown below, the outer jacket tube 120 may be included (as long as the dry air described below can be circulated so as to achieve its effect).

First, the air drying system will be briefly described. As described above, the corrosion prevention method according to the present invention can achieve sufficient rust prevention effects, but it is preferable to introduce an air drying system in addition to this, and when introducing this, it is preferable to use a structural cable that has been treated with the corrosion prevention method according to the present invention, because the air drying system can be suitably introduced. That is, in the corrosion prevention method according to the present invention, a structure can be realized in which dry air in the air drying system flows between the thin resin film (fluororesin (preferably ETFE sheet 160, ETFE tape 150)) and the structural cable (here referring to multiple cable wires 110 wrapped around the steel wire bundle 130).

The air supply drying system is a system that realizes more effective moisture blocking. For example, dry air is produced by removing salt and other elements from the outside air using air supply equipment installed on the main tower and stiffening girder of a suspension bridge, and the dry air is passed through an air supply pipe and sent into the structural cable 100. Moist air that has passed through the gaps in the structural cable 100 is exhausted from the exhaust bar and the tower top/anchorage saddle, keeping the inside of the structural cable 100 constantly dry. In the air supply equipment, a filter unit is installed to remove dust and salt from the outside air, and the outside air is dried by a dehumidifier, pressurized by an air supply blower, and sent to the cable. Here, it has been confirmed through literature and tests that the cable wire 110, which is a steel wire (steel material), hardly corrodes at a relative humidity of 60% or less. Therefore, in order to reliably maintain a relative humidity of 60% or less, it is preferable to set the management target value of the dry air in the cable to a relative humidity of 40%.

In the case shown in FIG. 3, in a structural cable 104 on which the anticorrosive method of the present invention has been applied, the dry air supplied from outside the structural cable 104 is divided into dry air A (1) that flows through the space between the resin thin film (here, ETFE sheet 160) and the structural cable (here, referring to multiple cable wires 110 wrapped around the steel wire bundle 130), and dry air A (2) that flows through the gaps between the multiple cable wires 110 wrapped around the steel wire bundle 130. This results in low air flow resistance, and the entire cable wires 110 in the structural cable 104 can be effectively dried without partial bias without causing extreme differences in the amount of air flow within the structural cable 104.

In the case shown in FIG. 4, in a structural cable 100 on which the anticorrosive method of the present invention has been applied, the dry air supplied from outside the structural cable 100 is divided into dry air A (1) that flows through the space between the resin thin film (here, ETFE tape 150) and the structural cable (here, referring to multiple cable wires 110 wrapped with steel wire bundles 130), and dry air A (2) that flows through the gaps between the multiple cable wires 110 wrapped with steel wire bundles 130. This results in low air flow resistance, and the entire cable wires 110 in the structural cable 100 can be effectively dried without partial bias without causing extreme differences in the amount of air flow within the structural cable 100.

As described above, when a structural cable is subjected to the corrosion prevention method of the present invention, the rust prevention effect can be further enhanced by suitably introducing an air drying system as in this modified example.
It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

The present invention relates to a corrosion prevention technology for structural cables exposed outdoors and used in suspended structures such as suspension bridges and cable-stayed bridges, and is particularly suitable for a corrosion prevention method that aims to extend the life of such structural cables rather than replacing them when they become corroded (especially when the corrosion is minor and replacement is difficult).

100, 102, 104, 202 Structural cable undergoing anticorrosion treatment 110 Cable wire 120 Sheath tube 150, 152 ETFE tape 160 ETFE sheet
162 Sheet end 252 Synthetic rubber tape

Claims (8)

A corrosion protection method for existing structural cables exposed outdoors or new structural cables exposed outdoors, which is used in suspended structures including suspension bridges and cable-stayed bridges, comprising:
The structural cable is wrapped and covered with a visible transparent and weldable resin thin film;
A corrosion protection method for structural cables, characterized in that a substance that visualizes the intrusion of moisture or humidity between the structural cable and the thin resin film is placed between the structural cable and the thin resin film, and the intrusion is visually confirmed through the transparent thin resin film using the substance . The corrosion protection method for structural cables according to claim 1, characterized in that the resin is a fluororesin. The corrosion protection method for structural cables according to claim 1 or 2, characterized in that the resin thin film is tape-shaped, and the tape-shaped resin thin film is overlapped over at least a portion of the tape width and spirally wound around the structural cable, thereby enveloping and covering the structural cable with the tape-shaped resin thin film. The corrosion protection method for structural cables according to claim 1 or claim 2, characterized in that the resin thin film is in the form of a sheet, and the sheet-like resin thin film is wrapped around the structural cable so that the sheet-like resin thin film forms a single-layered tube, and the ends of the sheet that are perpendicular to the longitudinal direction of the structural cable are overlapped, thereby wrapping and covering the structural cable with the sheet-like resin thin film. The corrosion protection method for structural cables according to claim 3 or 4, characterized in that after the resin thin films are overlapped, the overlapped portions are heated and thermally welded. A corrosion protection method for structural cables as described in any one of claims 1 to 5, characterized in that a substance that changes color in response to moisture or humidity is placed between the structural cable and the resin thin film. A structural cable exposed outdoors and used in suspended structures including suspension bridges and cable-stayed bridges, which has been treated with the corrosion prevention method described in any one of claims 1 to 6. The structural cable according to claim 7, which is provided with a structure in which dry air supplied from outside the structural cable flows between the resin thin film and the structural cable.