JP7312781B2 - PC steel material evacuation decompression rust prevention method and PC structure construction method using the same - Google Patents

Description

Article 30, Paragraph 2 of the Patent Law applied Tobishima Technical Report 2020 No. 68 (issued on November 30, 2020)

The present invention relates to a PC steel ventilation decompression rust prevention method and a PC structure construction method using the same, and more particularly to a PC steel ventilation evacuation decompression rust prevention method and a PC structure construction method using the same, which enables the PC steel to be rust-proofed during a predetermined period from the installation of the PC steel to the filling of grout by venting and decompressing the inside of the sheath through which the PC steel is inserted to maintain the reduced pressure state.

In the construction of a PC structure, a method of giving the concrete prestress is that a concrete is placed so that the PC steel material is tense in advance, and a concrete is placed so that the PC steel material is built -in, and the PC steel material is solved after the concrete, and a hollow tube called a seas, which is called a seas that inserts PC steel material. There is a post -tension system in which concrete is placed so that the sheath is built -in, a PC steel material is inserted into the sheath after the concrete is cured, and the PC steel material is tense, and both ends are established with fixing tools.
In the case of the post-tension method, the PC steel material in the sheath is exposed to the air when it is fixed under tension, and the oxidation of the PC steel material progresses, so it is necessary to inject a filler called grout into the sheath immediately after fixing to prevent the PC steel material from rusting.

Prestressed concrete (PC) is widely applied in large-scale construction works where high strength is required. One of the representative PC structures is a bridge. There are various types of bridges, but in the case of a cantilever construction method, the bridge girders are gradually extended in a cantilever shape on both sides of the bridge pier. Normally, construction sections are set, and the bridge girders are extended while being reinforced with PC steel materials for each construction section, and the rust prevention of the PC steel materials by grouting is also completed within one construction section. Therefore, in order to extend the bridge girders to the required length, it is necessary to prepare grout for at least the number of construction sections required.

Grout requires time and effort to prepare for mixing, kneading, testing, etc., and it has a large effect on the properties, so sufficient attention must be paid to the working temperature. For this reason, there is a need to reduce the preparation of grout as much as possible, such as performing grout filling work for a plurality of construction sections at once. As for the working temperature, for example, at a work site in the extremely cold winter, it is necessary to take temperature countermeasures such as working while keeping the grout warm.
In order to meet these needs, it is essential to develop a rust-preventing technology that prevents the prestressing steel from rusting for a predetermined period of time after the prestressing steel is installed, tensioned, and fixed until the grout is filled. As a rust prevention technique for meeting such needs, a technique such as Patent Document 1 has been proposed.

Patent Literature 1 discloses a rust-preventing structure that realizes rust prevention of the PC steel material in the sheath by inserting a long molded body containing a volatile rust inhibitor along the PC steel material into the sheath through which the PC steel material is inserted. According to the invention described in Patent Document 1, it is expected that the strained PC steel material in the sheath can be easily and reliably rust-proofed until it is filled with grout.

However, in the invention described in Patent Document 1, since it is necessary to prepare a long volatile rust inhibitor-containing molded body, construction costs are required for this, and in addition, after installing the PC steel material, it is necessary to insert the volatile rust inhibitor-containing molded body into each sheath and remove the volatile rust inhibitor-containing molded body that has been inserted before filling with grout. In addition, since the rust inhibitor is vaporizable, there is also a problem in terms of management, such as the need to store the vaporizable rust preventive agent-containing molded article after it is manufactured and before it is used.
Therefore, it is desired to provide a rust-preventing method for PC steel that can prevent rusting of PC steel during a predetermined period from installation of PC steel to grout filling without using a special rust-preventive agent such as a compact containing a volatile rust-preventive agent.

Japanese Patent Application Laid-Open No. 2002-371669

The present invention has been made in view of the problems in the above-described conventional rust prevention method for PC steel materials, and an object of the present invention is to provide a PC steel material evacuation and depressurization rust prevention method and a PC structure construction method using the same, which can prevent the PC steel material from rusting during a predetermined period from the installation of the PC steel material to the filling of the grout by venting and decompressing the inside of the sheath through which the PC steel material is inserted to maintain the reduced pressure state.

To achieve the above object, the method for preventing corrosion of prestressed concrete steel by ventilating and reducing pressure according to the present invention is a post-tension type prestressed concrete structure construction method in which a sheath through which the prestressing steel is inserted is hardened with concrete, then the prestressed concrete is tensioned and then grout is filled and fixed to fix the prestressed concrete. An interconnection step of connecting the exhaust hoses of each of the sheaths of each of the plurality of PC steel materials after tension is applied to the PC steel members after the tension is completed, and connecting the exhaust hoses of the sheaths of the sheaths interconnected by the exhaust hoses to a vacuum pump to collectively evacuate and decompress the interior of the plurality of sheaths interconnected by the exhaust hoses to maintain the decompressed state. It is characterized by having a venting and depressurizing stage.

After the evacuation/decompression step for one construction section is completed, the sheath fixing step, the closing step, the interconnecting step, and the evacuation/decompression step are repeatedly performed for each new construction section until a predetermined construction section is reached, and the vacuum pump preferably evacuates and decompresses the inside of the sheath for a plurality of construction sections collectively to maintain the decompressed state.

In order to achieve the above object, the method for constructing a prestressed concrete (PC) structure using the PC steel ventilation, depressurization, and rust prevention method according to the present invention further comprises a grouting step of stopping the vacuum pump immediately after the PC steel ventilation, decompression, and rust prevention method for one construction section or a plurality of construction sections is completed, or after a predetermined period of time, and filling all the sheaths connected to the vacuum pump with grout.

According to the PC steel removal reduction pressure prevention method according to the present invention, the mouth of each exhaust hose that leads to the opening of the sheath is closed, and the tension has ended with a plurality of sheath exhaust hoses of the PC steel material, then connected to the vacuum pump, and the PC steel material is rusted by maintaining the decompression state. Because it is possible, it is no longer necessary to prepare and fill the ground for each construction section, and the construction period is reduced accordingly, improving the productivity of the PC structure. Also, since the vacuum pump to be used can be used in common with the vacuum pump used for pressure reduction to prevent incomplete filling during grout filling work, there is no need to prepare a special device for rust prevention.

According to the PC steel material evacuation decompression rust prevention method and the PC structure construction method using the same according to the present invention, it is possible to prevent rusting of the PC steel material for a long period of time by maintaining the decompressed state in the sheath with a vacuum pump.

FIG. 2 is a diagram schematically showing a configuration for venting the inside of the sheath in the PC steel material venting decompression rust prevention method according to the embodiment of the present invention; FIG. 2 is a diagram showing a structural example of a fixing portion of the PC steel material of FIG. 1; FIG. 4 is a diagram schematically showing a connection method of an exhaust path in the PC steel material venting, decompression rust prevention method according to the embodiment of the present invention. FIG. 4 is a diagram showing a part of changes over time of the environment inside the sheath in a demonstration experiment of the PC steel material evacuation decompression rust prevention method according to the embodiment of the present invention. FIG. 5 shows the surface condition of the PC steel material after the demonstration experiment of FIG. 4, FIG. 5(a) shows the surface condition of the PC steel material when the reduced pressure state in the sheath is maintained, and FIG. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow chart for explaining a PC steel material evacuation method and a PC structure construction method using the same according to an embodiment of the present invention.

Next, a concrete example of a form for carrying out the PC steel material evacuation decompression rust prevention method and the PC structure construction method using the same according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram schematically showing a configuration for venting the inside of a sheath in a PC steel material venting, depressurization and rust prevention method according to an embodiment of the present invention. FIG. 1 omits the piers and shows the bridge pier head A and the bridge part in a state where the overhang erection work from the pier head A to the first construction section B and the second construction section C has progressed to the left and right.

Referring to FIG. 1, in the prestressing steel material evacuation decompression rust prevention method according to the embodiment of the present invention, a plurality of sheaths 20, which are hollow pipes, are embedded in concrete 5 in a manner that crosses the pier head A, and the prestressing steel materials 10 are inserted through the sheaths 20, and both ends of each prestressing steel material 10 are fixed by fixing portions 40. In addition, in the vicinity of both ends and in the middle of the sheath 20, an injection hose 31 used when injecting a filler called grout around the PC steel material 10 or an exhaust hose 30 for preventing cavities during grout injection is connected. Among the plurality of exhaust hoses 30, some are interconnected by hose joints 32, others are connected to the vacuum pump 50 via branch joints 51, and the tips of the injection hose 31 and the rest of the exhaust hoses 30 are closed with caps 33.

In the post-tension type PC concrete structure, after concrete 5 is placed and hardened, the PC steel material 10 is inserted into a sheath 20 embedded in the concrete 5, and then the PC steel material 10 is fixed under tension to apply compressive stress to the concrete 5. - 特許庁As a result, the tensile stress caused by the bending moment generated in the concrete 5 on the upper surface of the pier column head A is alleviated during the construction of the bridge extending in the state of a cantilever beam, and after completion, thereby improving the strength of the structure.

The post-tension type PC steel material 10 is exposed to the atmosphere inside the sheath 20 when it is inserted into the sheath 20 or when it is firmly fixed under tension, and there is a risk that water such as rainwater may enter from the opening of the sheath 20. If a long period of time passes in this state, the PC steel material 10 will oxidize, and as the oxidation progresses, strength reduction and disconnection may occur. Therefore, in the usual construction method, after the PC steel material 10 is tense and fixed, the sheath 20 is quickly filled with grout and hardened to prevent the PC steel material 10 from being oxidized. In the bridge construction that extends while placing the concrete 5 on site, the entire construction section is divided into several construction sections, and the PC steel material 10 is tensioned and fixed in each construction section every time the construction section is completed, so grout filling is also performed for each construction section. Grout takes time and effort to prepare for mixing, kneading, testing, etc. before filling, and the quality tends to deteriorate if the working temperature is too high or too low.

In the PC steel material evacuation decompression rust prevention method according to the embodiment of the present invention, the concrete 5 is poured and hardened around the sheath 20 placed, and the PC steel material 10 is inserted and placed in the sheath 20 embedded in the concrete 5. Then, the mouths of the exhaust hoses 30 and the injection hoses 31 connected to the openings of the sheath 20 are quickly closed to prevent water and air from flowing into the sheath 20. After that, tension is applied to the PC steel material 10, and then the exhaust hoses 30 of the sheaths 20 of the plurality of PC steel materials 10 whose tension is finished are connected to each other, and the exhaust hoses 30 of any of the plurality of sheaths 20 mutually connected by the exhaust hose 30 are connected to a vacuum pump 50 to collectively evacuate and depressurize the interior of the plurality of mutually connected sheaths 20 to maintain the decompressed state, thereby preventing the PC steel materials 10 from rusting for a predetermined period until the grout is filled. is a method of doing

In the PC steel material evacuation decompression rust prevention method according to the embodiment of the present invention, the above-described fixing of the sheath 20 to the evacuation/decompression are repeated for each construction section, so that the PC steel materials 10 in a plurality of construction sections can be collectively maintained in a rust-proof state for a predetermined period.
Further, in the method for constructing a PC structure using the PC steel air evacuation decompression rust prevention method according to the embodiment of the present invention, after maintaining the rust prevention state for a predetermined period by the PC steel air evacuation decompression rust prevention method, the vacuum pump 50 is stopped immediately after the completion of the PC steel air evacuation decompression rust prevention method for one construction section or a plurality of construction sections or after a predetermined period until the season when the working temperature environment improves, and all the sheaths 20 connected to the vacuum pump 50 are filled with grout. It is a method to maintain 0 rust prevention.

As described above, the PC steel material evacuation decompression rust prevention method and the PC structure construction method using the same according to the present invention are a method in which the inside of the sheath 20 is vacuumed all at once to maintain the reduced pressure state, thereby freely selecting the timing of grout filling and grout filling can be performed collectively for a plurality of construction sections.

FIG. 1 illustrates a state in which three types of sheaths 20 having different lengths are provided in parallel in the depth direction of the figure: sheaths 20 with anchoring portions 40 positioned at both ends of the pier column head A, sheaths 20 with anchoring portions 40 positioned at the ends of the left and right first construction sections B, and sheaths 20 with anchoring portions 40 positioned at the ends of the left and right second construction sections C. When the sheath 20 is fixed, the sheath 20 having a length that fits in one construction section is installed so that the end is exposed, the concrete 5 is cast and hardened, and the exposed end of the sheath 20 is connected to a new sheath 20 to be used when constructing the next construction section, and this is repeated to extend to the required length. Thereby, sheaths 20 having different lengths are fixed.

Each sheath 20 is provided with a plurality of openings, an injection hose 31 for injecting grout and an exhaust hose 30 are connected to the opening at one end of the sheath 20, and the exhaust hose 30 is connected to the opening at the other end. In addition, the exhaust hose 30 is also provided at the opening in the intermediate portion where air is likely to accumulate during grout injection. After inserting the PC steel material 10 into the sheath 20 and arranging it, the injection hose 31 and the exhaust hose 30 connected to these openings are closed, in which case a cap 33 such as a joint cap is used. Next, tension is applied to the PC steel material 10 to fix it, and the exhaust hoses 30 of the sheaths 20 of each of the plurality of PC steel materials 10 that have been tensioned are connected to each other. For the connection of the exhaust hoses 30, for example, as shown in FIG.

Among the sheaths 20 of three different lengths shown in FIG. 1, for example, two sheaths 20 having anchoring portions 40 located at both ends of the pier column head A have exhaust hoses 30 at the left end connected by a hose joint 32, and at the right end, one exhaust hose 30 is closed by a cap 33, and the other exhaust hose 30 is connected to a vacuum pump 50 via a branch joint 51. In addition, the injection hose 31 connected to the two sheaths 20 and the exhaust hose 30 at the intermediate portion are also closed with the cap 33 . With such a connection, the two sheaths 20 with the fixing parts 40 positioned at both ends of the pier head A become like a series-connected pipe with one end closed, and are collectively decompressed by the vacuum pump 50. Similarly, two parallel sheaths 20 of other lengths are also connected in series and are collectively decompressed by the vacuum pump 50 . The vacuum pump 50 used here may be the vacuum pump 50 used in the subsequent grout filling process, thereby eliminating the need for an additional device for rust prevention of the PC steel material 10 .

The branch joint 51 is connected to the vacuum pump 50, and the main body portion is provided with a plurality of connection ports each having an on-off valve and communicating inside the branch joint 51. By opening and closing the on-off valve, the exhaust hose 30 connected to the connection port can be selectively decompressed. By having a plurality of connection ports, for example, the exhaust hose 30 connected to each construction section can be connected to the connection port, and air can be removed and depressurized collectively for each construction section. FIG. 1 shows a state where each of the bridge pier column head A, the first construction section B, and the second construction section C is connected to the connection port of the branch joint 51 .

When three or more sheaths 20 are arranged in one construction section, the exhaust hoses 30 may be connected in order so that the sheaths 20 are in a series connection relationship, or a joint such as a branch joint 51 that can be branched may be used to connect the exhaust hoses 30 at one end and the other end of the sheaths 20 together so that the sheaths 20 are in a parallel connection relationship, and one of them may be connected to the vacuum pump 50 via the branch joint 51.

The arrangement and number of the sheaths 20, the arrangement and number of the exhaust hoses 30 and the injection hoses 31 shown in FIG.

FIG. 2 is a diagram showing a structural example of the fixing portion of the PC steel material in FIG.
Referring to FIG. 2, anchoring portions 40 are formed at both ends of the sheath 20 and the PC steel material 10 inserted into the sheath 20, and a grout cap 41 is attached to each anchoring portion 40 so as to cover the end portion of the PC steel material 10 after the anchoring is completed. The fixing part 40 shown on the left side in the drawing is a structural example of the side that tensions the PC steel material 10 , and the fixing part 40 shown on the right side is a structural example of the fixed end side that fixes the PC steel material 10 . The PC steel material 10 shown in FIG. 2 has a structure in which twisted wires are bundled, and each twisted wire is dispersed and fixed or tensioned at the fixed portion at the end.

In the fixing part 40 at the fixed end, after each strand of the PC steel material 10 is inserted into each through hole of the anchor plate 43 formed with a plurality of through holes, a crimping grip 44 having an outer diameter larger than the diameter of the through hole is attached to the tip of each strand, so that the PC steel material 10 is fixed so as not to come off even if the PC steel material 10 is tensioned at the other end.

In the fixing part 40 on the tensioning side, tension is applied while the space between the female cone 46 and the male cone 45 is circumferentially expanded, and then the load is released while the male cone 45 is pressed, whereby fixing is performed while maintaining the tension.
Fixing methods other than those described above can be performed by various methods using various fixing tools, but any tensioning method may be used in the PC steel material evacuation and decompression rust prevention method according to the embodiment of the present invention.

In FIG. 2 , an injection hose 31 is connected to an opening for injecting grout near the end of the sheath 20 on the tensioning side, and the injection hose 31 extends to the outside of the concrete 5 . A cap 33 is attached to the tip of the injection hose 31 so as to prevent rainwater or the like from entering. A grout cap 41 having two openings is attached to the fixing portion 40. One opening is closed by a plug 42, and the exhaust hose 30 is connected to the other opening. The exhaust hose 30 is connected to any exhaust hose 30 of another sheath 20 via a hose joint 32 .

A grout cap 41 having a similar configuration is also attached to the fixing portion 40 on the fixed end side. The exhaust hose 30 connected to the grout cap 41 on the fixed end side is connected to a branch joint 51 connected to the vacuum pump 50 via a check valve 52 . By vacuuming with the vacuum pump 50 in this state, the pressure in the sheath 20 in the figure and the other sheath 20 connected via the hose joint 32 is reduced, and this state is maintained while the vacuum pump 50 continues to operate.

After the lapse of a predetermined period, for example, after completion of all the planned work in a plurality of construction sections or after waiting until the season when the environmental temperature for grout injection becomes appropriate, grout is injected to prevent the prestressing steel material 10 from rusting with the grout. When injecting the grout, the vacuum pump 50 is stopped or the open/close valve of the branch joint 51 is closed before injecting the grout from the injection hose 31 . At this time, by starting grout injection in a state in which the pressure inside the sheath 20 is reduced, an effect of suppressing the occurrence of air pockets in the grout is expected.

FIG. 3 is a diagram schematically showing a connection method of an exhaust path in the PC steel material evacuation decompression rust prevention method according to the embodiment of the present invention. Although FIG. 1 illustrates a case where there are two sheaths 20 having the same length in the depth direction, the number of sheaths 20 is not limited to this in the embodiment. FIG. 3 shows the connection for rust prevention of PC steel materials 10 installed over the bridge pier column head A, the first construction section B, the second construction section C, and the third construction section D.

Referring to FIG. 3, four sheaths 20 are arranged symmetrically across the center line. Although the injection hose 31 of each sheath 20 and the exhaust hose 30 at the intermediate portion of the sheath 20 are omitted, the ends of these hoses are closed with caps 33 in the evacuation and decompression stages.

Focusing on the four sheaths 20 on the left side, the exhaust hoses 30 of two adjacent sheaths 20 are connected by a hose joint 32, and the four sheaths 20 are connected in series as an exhaust path. The exhaust hose 30 of the sheath 20 at the left end, which is one end of the series connection, is connected to a branch joint 51 via a check valve 52 . The exhaust hoses 30 of the sheaths 20 of the pier column head A, the first construction section B, the second construction section C, and the third construction section D are individually connected to other terminals of the branch joint 51, respectively. The branch joint 51 is connected to a vacuum pump 50, whereby the sheath 20 in the path connected to the branch joint 51 is evacuated and decompressed.

A vacuum gauge 53 is connected to the exhaust hose 30 of the sheath 20 closer to the center line, which is the other end of the series connection. All of the exhaust hoses 30 other than the exhaust hoses 30 to which the hose joint 32, the vacuum gauge 53 and the like are connected are closed with caps 33 at their ends.

Although the four sheaths 20 are connected in series in the embodiment of FIG. 3, in other embodiments the sheaths 20 are connected in parallel. In other embodiments, serial connection and parallel connection may be used together. For example, two sheaths 20 may be connected in parallel, and then the connected two sheaths 20 may be connected in series.

FIG. 4 is a diagram extracting and showing a part of changes over time of the environment inside the sheath in the demonstration experiment of the PC steel material evacuation decompression rust prevention method according to the embodiment of the present invention.
In the demonstration experiment, concrete 5 was placed around a sheath 20 of a predetermined length to prepare a quadrangular prism-shaped specimen. Next, after inserting the PC steel material 10 into the sheath 20 and setting a sensor for measuring the air pressure and humidity inside the sheath 20, the air pressure and humidity inside the sheath 20 were measured over time for about four months from April to August by closing everything except the exhaust hose 30 connected to the vacuum pump 50 and operating the vacuum pump 50.

In FIG. 4, the vertical axis is atmospheric pressure or internal humidity, and the atmospheric pressure is indicated by gauge pressure. The horizontal axis is the number of days, and indicates 17 days, which is part of the period of the demonstration case. During this period, the air pressure fluctuated periodically around -98 kPa and did not reach -94 kPa at maximum. Humidity fluctuated periodically around 3%, and was about 12% at maximum.

FIG. 5 is a diagram showing the surface condition of the PC steel material after the demonstration experiment of FIG. 4, FIG. 5(a) is a surface condition of the PC steel material when the reduced pressure state in the sheath is maintained, and FIG.
Two specimens were produced, one specimen was evacuated and depressurized by the vacuum pump 50, and the other specimen was opened to the atmosphere.

Referring to FIG. 5(a), it was confirmed that the surface of the PC steel material 10 did not change from the initial state when the pressure-reduced state in the sheath 20 was maintained, and that the occurrence of rust could be prevented. On the other hand, in the PC steel material 10 stored with the inside of the sheath 20 open to atmospheric pressure, rust 11 was found to occur as shown in FIG. 5(b).

In the demonstration experiment, in addition to the demonstration experiment described with reference to FIGS. 4 and 5, an experiment was also conducted in which the exhaust hoses 30 of the sheaths 20 at one ends of the two specimens were connected to each other to form an exhaust path connected in series, one end of the exhaust path was closed, and the other end was evacuated by the vacuum pump 50. In this experiment, the surface of the PC steel material 10 was wetted with water and then inserted into the sheath 20. The pressure inside the sheath 20 was about 0.1 to 0.2 atmospheres (a gauge pressure of about -80 kPa or less), and the sheath was left for about 3 months.

FIG. 6 is a flow chart for explaining a PC steel material evacuation method and a PC structure construction method using the method according to an embodiment of the present invention.
Referring to FIG. 6, before placing the concrete 5 in the first construction section in step S600-1, the sheath 20 is installed at a predetermined position in the concrete formwork, and then the concrete 5 is placed around the sheath 20 and hardened to fix the sheath 20. The sheath 20 is exposed from the concrete 5 and fixed so that a fixing part 40 can be installed when the sheath 20 is fixed by the length up to the end of the first construction section, and a connection joint can be attached when the sheath 20 is extended to the next construction section. In addition, when there is an injection hose 31 or an exhaust hose 30 connected to an opening other than the end of the sheath 20, each hose (30, 31) is fixed so that at least the vicinity of the tip is exposed to the outside of the concrete 5 so that grout can be injected later.

After the concrete 5 hardens, the PC steel material 10 is inserted into the sheath 20, which is fixed to the end of the first construction section, and the injection hose 31 and the exhaust hose 30 connected to the opening of the sheath 20 are closed by closing (step S610-1).

Next, in step S620-1, the PC steel material 10 is tensioned and fixed, and after fixing, the fixing part 40 is covered with a grout cap 41 and fixed, and any of the exhaust hoses 30 connected to the sheath 20 including the exhaust hose 30 connected to the grout cap 41 is connected to any of the exhaust hoses 30 of the other sheath 20. When there is another sheath 20 other than the sheath 20 connecting the exhaust hoses 30, the exhaust hose 30 of the sheath 20 connecting the exhaust hoses 30 is connected to the exhaust hose 30 of the other sheaths 20.例文帳に追加In this way, all the sheaths 20 of the PC steel material 10 fixed to the end of the first construction section are connected with one of the exhaust hoses 30 to form one exhaust path. The connection between the exhaust hoses 30 at this time may be such that the plurality of sheaths 20 are connected in series with each other, or may be connected in parallel with each other.

Finally, in step S630-1, one of the exhaust hoses 30, which are one end of the exhaust path, is connected to the branch joint 51 connected to the vacuum pump 50, and the tip of the remaining exhaust hoses 30 including the other end of the exhaust path is blocked with the cap 33 to prevent water and outside air from entering. It is best if the pressure in the sheath 20 is low, that is, the degree of vacuum is high. Therefore, even if the vacuum pump 50 does not operate continuously, a pressure sensor may be installed in the sheath 20, and control means may be further provided to operate the vacuum pump 50 when the pressure reaches a certain level or higher so as to maintain the pressure at 0.2 atm or less.

In steps S600-1 to S630-1, the antirust work by venting and decompressing the first construction section is completed. Here, the first construction section is not limited to the construction section following the bridge pier column head A shown in FIG. As shown in FIG. 1, when there is a prestressing steel material 10 anchored in the pier capital A, the first construction section corresponds to the pier capital A.

Grouting may be performed by injecting grout to prevent rust by grouting when the rust preventive work by vacuum depressurization in the first construction section is completed or after this state is maintained for a predetermined period. In this case, steps similar to step S600-1 to step S630-1 are repeated each time work for one construction section is performed. Steps S600-n to S630-n are similarly performed in the n-th construction section (n is a natural number of 2 or more), which is a predetermined construction section.
After completion of step S630-n or after a predetermined period of time has passed after completion of step S630-n, grout is injected in step S640 to fill the sheath 20 with grout.

The grouting operation of step S640 is basically the same as a normal grouting operation. However, unless the vacuum pump 50 is stopped and the cap 33 of either the exhaust hose 30 or the injection hose 31 is removed to open it, the inside of the sheath 20 is maintained in a reduced pressure state.

Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the technical scope of the present invention.

5 Concrete 10 PC steel material 20 Sheath 30 Exhaust hose 31 Injection hose 32 Hose joint 33 Cap 40 Fixing part 41 Grout cap 42 Plug 43 Anchor plate 44 Crimp grip 45 Male cone 46 Female cone 50 Vacuum pump 51 Branch joint 52 Check valve 53 Vacuum gauge A Bridge pier column head B First construction section C Second construction section

Claims (2)

A rust prevention method for PC steel materials when constructing a post-tension type PC structure in which a sheath through which the PC steel materials are inserted is solidified with concrete, and then the PC steel materials are tensioned and then grout is filled and fixed, comprising:
A sheath fixing step of fixing a sheath of PC steel material for placing concrete for one construction section and applying prestress to the construction section;
a closing step of immediately closing the mouths of the exhaust hoses and the injection hoses connected to the openings of the sheath after the PC steel material is inserted into the sheath and arranged;
an interconnecting step of applying tension to the PC steel material and then connecting the exhaust hoses of each of the sheaths of each of the plurality of PC steel materials whose tension is finished;
a venting/depressurizing step of connecting the exhaust hose of any one of the sheaths mutually connected by the exhaust hose to a vacuum pump and collectively venting/depressurizing the plurality of sheaths mutually connected by the exhaust hose to maintain the decompressed state ;
After the evacuation/decompression step for one construction section is completed, repeating the sheath fixing step, the closing step, the interconnecting step, and the evacuation/decompression step for each new construction section until a predetermined construction section is reached,
A method for removing air, reducing pressure, and preventing corrosion of PC steel materials, wherein the vacuum pump removes and depressurizes the interior of the sheath for a plurality of construction sections collectively to maintain a decompressed state . A method for constructing a PC structure using the PC steel material evacuation decompression rust prevention method according to claim 1 ,
A method for constructing a PC structure, further comprising a grout filling step of stopping the vacuum pump immediately after the PC steel material evacuation decompression rust prevention method for a plurality of construction sections is completed or after a predetermined period of time, and filling all the sheaths connected to the vacuum pump with grout.

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